User:Haowen Wan/Win share

Win share is a metric that estimates the number of wins a player produces for his team throughout the season. Each win share a player earns suggests their overall efforts have contributed one win to the team’s total record for the season. Win share is divided into OWS(offensive win share), DWS(defensive win share), Overall win share. Win Shares was originally designed by Bill James in his book " Win Share" to measure the number of wins a player contributed in baseball game. Dean Oliver later introduced Win Shares to the basketball world to measure the number of wins a player contributed to a team. It's divided into the Offensive and Defensive parts, the Offensive win Share and the DWS. Win share is a common statistics to measure how a player contributes to a team win in NFL, NBA, MLB, NHL.

Win Share (Book)
The idea of win share was firstly introduced by Bill James and Jim Henzler, published by STATS, Inc. in 2002. The book use a saber-metric method to evaluate the contribution of each player made to their team's overall performances. The book mainly focus on introducing the complex formulas to calculate the number of win share in baseball world. Moreover, the book has suggested various way of rating baseball players and show their efficiency.

Win Share (statistics)
In the book "win share", Bill firstly introduces the concept of win shares as a statistics to show how to apply the concept of saber-metrics to assess the impact of player performance in a combination of several areas, including offensive, defensive, and pitching, to the overall performance of their team. A Win Share is a single number that covers the whole shooting match: offense, defense and, if the player in question is a pitcher, pitching. What is especially neat about it is that it takes into account context. A player's home park advantage/disadvantage is factored into the equation as is the era in which he played or is playing.

By definition, the common approach to calculate Win share is that it represent one-third of the team wins. For example If a team wins 60 games in a season, then the player would share 180 win shares, and the 180 win shares would dividend into offense and defense.

On a team with equal offensive and defensive prowess, hitters receive 48% of the win shares and those win shares are allocated among the hitters based on runs created. An estimation is then made to decide what amount of the defensive credit goes to pitchers and what amount goes to fielders. Pitching contributions typically receive 35% (or 36%) of the win shares, defensive contributions receive 17% (or 16%) of the win shares. The pitching contributions are allocated among the pitchers based on runs prevented, the pitchers' analogue to runs created. Fielding contributions are allocated among the fielders based on a number of assumptions and a selection of traditional defensive statistics.

After Bill James bring win shares to baseball world, more and more professional leagues start to accept the concept of win share and bring win shares to other leagues.

Who bring win share to NBA
Dean Oliver of Director of Quantitative Analysis, Denver Nuggets quickly recognized the value of proportionally dividing credit for team success in basketball, where individual players have a massive influence relative to many other team sports. Dean Oliver write a book " Basketball on Paper" which combines the statistical analysis of Bill James in baseball with the coaching philosophy of Dean Smith to arrive at a unique tool to evaluate the player contribution.

After Dean Oliver has improved the concept of win shares in the book "Basketball on Paper", Justin Kubatko of Basketball-Reference.com quickly recognized the value of proportionally dividing credit for team success in basketball, where individual players have a massive influence relative to many other team sports.Furthermore, Kubatko created a new formula using readily available player stats to calculate the number of wins each player contributes to the team each season, and basketball win shares were born

The 4 category of win share
There are four types of win share: OWS( offense win share), DWS( defense win share), Overall WS( overall win share), WS/48( win share per 48 minutes)

The significance of OWS/DWS
Win share provide a chance for manger to see where the player are making most impact, painting a more detailed picture of how their presence on the court might affect the game.

The significance of WS/48
Win Share heavily rely on the minutes player play, more minutes means higher possibly of getting higher win share. The starter's win shares are flatted by additional time they spend on the court. Thus WS/48 give player a chance to compete with each other if they all played the same number of minutes. Moreover WS/48 is a better method to measure whether to pick one substitute player if the starter get injured.

The reason why NBA use Win share in daily stats
Win share is a stats combing different indicator including rebound, assist, score, steal and etc. Such overall review of one player's performance reflects the contributions a player to the team. It is quite useful for managers to considering the impacts of lineup changes following injury or trades.

How to calculate win share in NBA(formula)
Win share is cumulative and will accumulate over the season. The accumulated WS of each player represents the total wins of the team, and the estimated number of wins contributed by the player. A negative win share happens in two situations, one is when the teams continues losing during the season, a bad team record would lead players getting negative win shares, another is when a player contributes few to a team win. There are three categories of win share: OWS( Offensive win share), DWS(Defensive win share), Overall win share.

OWS(Offensive win share)
The offensive win share represents the player efficiency of offense in a game.

To calculate offensive win shares, you first need to find points produced and offensive possessions for the player you’re evaluating. You can use these numbers to calculate marginal offense and marginal points per win, which are used to find the player’s offensive win share.

Math formula: $$Offsensive win share= marginal offense/ marginal points per win$$

where


 * Marginal Offense: A measure of how much better a player's scoring efficiency is than the league's average offensive efficiency.
 * $$marginal offense=points produced-0.92*(league points per possession)*(offensive possession)$$

where


 * 1) points produced: Represents all the scoring a player brings to a team on the offensive side per possession
 * 2) league points per possession: Represents the average of all the scoring player brings to a team on the offensive side per possession
 * 3) Offensive possession: how many offensive possession a team get in a game


 * Marginal Points Per Win: It represents the marginal point benefit needed for each win.
 * $$marginal points per win =0.32*(league points per win)*((team pace)/(league pace))$$

where


 * 1) league points per win: the average points that a team winning in the league

DWS(Defensive win share)
The defensive win share represents the player efficiency of defense in a game

To calculate defensive win shares, you need the defensive rating of the player you’re evaluating. Using this stat, you can calculate marginal defense and marginal points per win, which can then be used to find the player’s defensive win shares.

Math formula: $$(marginaldefense)/(marginalpointsperwin)$$

where


 * Marginal defense $$(playerminutesplayed/teamminutesplayed)*(teamdefensivepossession)*(1.08*(leaguepointsperpossession)-((defensiverating)/100))$$

where


 * 1) Player minutes played: how many minutes a player play in a game
 * 2) team minutes played:  the sum of every player from the same team play in a game
 * 3) team defensive possession: how many defensive possession a team get in a game
 * 4) league points per possession: Represents the average of all the scoring player brings to a team on the offensive side per possession
 * 5) defensive rating/100: how many points their opponent get when facing one's defense


 * Marginal points per win : $$0.32*(leagugepointspergame)*((teampace)/leaguepace$$

where

1. league points per win: the average points that a team winning in the league

Overall win share
the overall win share represents the player efficiency from both offense and defense side in the game

Math formula: $$Overall win share= Offensive win share+ Defensive win share$$

Win Share Per 48 minutes( WS/48)
Math formula: $$WS/48=48*(Win shares/Minutes played)$$

Where


 * Win shares: the total sum of OWS and DWS
 * Minutes play : the total minutes a player play on the court

Criticism of win share
== Top 40 of NBA & ABA Career Leaders and Records for Win Shares == Active players are in bold
 * Win share heavily rely on the total minutes a player spend on the court, usually more minutes player play, higher their win share would be.
 * Win share works as a player stats which estimates how much a player contribute to a team's wins. Thus, the teams' WS sum should equal to the team's wins. However, when we calculate WS, the score is built on the league average. Thus the WS for each team would vary from actual number of team wins.
 * DWS is not objective due to its calculating process. Calculating DWS heavily rely on defensive rating(DRtg), however, DRtg has been question whether a fair calculating process. Thus, problems of calculating may occur when using Defensive rating as one of its factor.
 * Win share favor a player on a successful team, because the calculating process involved with team statistics. Thus win share might be a problem when comparing two players if they play for different teams.
 * Win share is hard to evaluate an injured star, because a team wins should be heavily effected by lacking of a start who should contribute a lot to a team wins. Thus when calculating a WS for a injured star, the score at end usually is lower than actual score.

Win share in NHL
Win share also known as Point share in hockey, the win share in hockey attempts to evaluate each player's contribution to their team in three facets of the game: offensive, defensive, and goalie. For skaters, win share both qualify on offense side and defense side. Goalies only have score in goalie win shares