| Statistic | Description | Formula |
| BFP | Batters Facing Pitcher - simply the number of batters that come to plate against a pitcher Note: consistently available only from 1904 to present in NL, and 1907 to present in AL |
not applicable |
| Ratio | (Walks + Hits) per 9 Innings Pitched (aka WHIP*9) | 9*(H+BB)/IP |
| SO/BB | Strikeout to Walk Ratio - one of the best ways to measure a pitcher's effectiveness | SO/BB |
| SO+ | League adjusted Strikeouts per 9 innings - a measure of a pitchers strikeouts per 9 innings relative to the league average, 100 being average. Allows a comparison of strikeout ability across eras. For example, the raw career numbers are 5.34 K/9 for Walter Johnson and 8.61 K/9 for Roger Clemens. Clemens was much better, right? Not really. SO+ career are 155 for Big Train, 144 for the Rocket. So Johnson struck out 55% more batters than the league avg, while Clemens struck out 44% more than the lg avg. Not a definitive answer, but surely it allows a much better comparison than the raw numbers. |
100*(SO/9)/(lgSO/9) |
| BB+ | League adjusted Bases on Balls per 9 innings a measure of a pitchers BB per 9 innings relative to the league average, 100 being average. Allows a comparison of a pitcher's ability to avoid giving up a Walk (BB). Again, this value allows a much better comparison across eras than the raw numbers. Above 100 is always better, so in this case, a BB+ of 200 means the pitcher walked half as many batters per 9 innings as league average. |
100*(lgBB/9)/(BB/9) |
| ERA+ | League Adjusted ERA - a great indicator of performace relative to the league, 100 is average, so ERA+ of 125 is 25% better than the league average | 100*(lgERA/ERA) |
| PPF | Pitching Park Factor - the home park PPF for a pitcher. The PPF of each park is calculated once for each season. PPF of 100 is an average park, > 100 is a batter's park and < 100 is a pitcher's park. A PPF of 105 indicates that all things being equal, 5% more runs will be scored at that park than an average park. PPF is used to convert ERA+ into a park-adjusted value, *ERA+ (see below) Click here to see detailed information on the calculation of Park Factors at www.baseball-reference.com |
n/a |
| *ERA+ | League-adjusted, Park-adjusted ERA - normalize player ERA+ using player's PPF, home park Pitching Park Factor. This will adjust player's ERA+ depending on whether they played in a good hitter's park (PPF > 100) or a pitcher's park (PPF < 100). Helpful in player comparison by canceling out home park advantages and disadvantages, such as pitching in Coors Field vs. Comerica Park. | 1) *lgERA = lgERA*(PPF/100) 2) *ERA+ = 100*(*lgERA/ERA) |
| ERC | Component ERA - sabermetric formula that estimates a pitcher's ERA based on his stats Note: only valid from 1904-present in NL, 1907-present in AL (see BFP above) |
((0.89*(1.255*([H]-[HR])+4*[HR])+0.56*([BB]+[HBP]))*([H]+[HBP]+[BB])/[BFP])*9/[IP]-0.56 |
| ERC% | Component ERA Ratio - a ratio of Component ERA, what the pitcher's ERA should have been, to actual ERA. You may use this to determine if a pitcher was 'lucky' (ERC% > 100) or 'unlucky' (ERC% < 100). Be careful, though, as this is not definitive. Park effects and team defense account for some or all of the difference seen as well. Take it for what it is. | (ERC/ERA)*100 |
| Win Shares | Pitching Win Shares - this is the 'short form' version of Bill James' newest metric, Win Shares. Win Shares attempt to measure a player's performance in terms of number of games won. Every Win Share indicates 1/3 of a win contributed to the team. Adding up all players' win shares on a team, including batting, pitching, and fielding, will equal team wins x 3, by definition. The numbers shown in pitcher queries are Win Shares for pitching only. By definition, Win Shares cannot be less than zero. | ((1.5 x *lgERA - 1)*IP/9 - ER +SV)/3 |
| BABIP | Batting Average against for Balls In Play - the pitcher's opponents batting average allowed on balls put into play (not including HRs); invented by Voros McCracken, theorized as a statistic not in the pitcher's control. Later shown to actually be part of a pitcher's ability, at least in my opinion. See an excellent analysis of BABIP by Tom Tippett here. |
(Hits - HR)/(BFP - HR - BB - SO - HBP) |