Wins Above Replacement (WAR) is an all-inclusive statistic that aims to quantify all of a player’s contribution to their team in one, simple stat.
Wins Above Replacement does exactly what it sounds like: it tells you how many wins a team would be losing if they lost a player and had to replace him with a Triple-A guy or free agent — a replacement player.
Using Pythagorean Win Percentage, it was found that every 10 runs is equivalent to one team one. So when calculating WAR, when a player contributes 10 runs — whether it be on offense, defense or on the bases — it’s equivalent to a WAR value of 1.
For hitters, WAR is calculated using hitting (wRAA/wOBA), fielding (UZR), base running (UBR), positional value and playing time. It compares a player’s statistics to the rest of the league and adjusts for park effects. The hitting side of WAR is straight forward, as there is little argument that wOBA is the best stat to determine a hitter’s all around worth. The biggest issues with WAR for hitters are the inconsistency of fielding statistics and how much positional value factors into the equation.
The positional adjustment is particularly important, though. A stud offensive catcher might only be an average offensive player if were to play first base. WAR accounts for this.
The best way to calculate the defensive side of WAR is heaviliy debated, as some feel there is too much inconsistency in UZR, which is currently used as WAR’s defensive metric. FSR can also be used interchangeably with UZR if you feel fans can better tell how good a player is defensively.
Both FanGraphs (fWAR) and Baseball Reference (bWAR or rWAR) have versions of WAR. fWAR is more commonly used.
WAR can be used to find the value, in dollars, of a particular player by finding how much money the free agent market paid for 1 WAR. Normally, this number is around $5 million. So to found out how much a player is worth, multiply their WAR by $5 million — or whatever the value per win is for that year — and you have that player’s worth.