1.pitching.csv

nameGiven      Player's given name (typically first and middle)
yearID         Year
stint          player's stint (order of appearances within a season)
teamID         Team
lgID           League
W              Wins
L              Losses
G              Games
GS             Games Started
CG             Complete Games 
SHO            Shutouts
SV             Saves
IPOuts         Outs Pitched (innings pitched x 3)
H              Hits
ER             Earned Runs
HR             Homeruns
BB             Walks
SO             Strikeouts
BAOpp          Opponent's Batting Average
ERA            Earned Run Average
IBB            Intentional Walks
WP             Wild Pitches
HBP            Batters Hit By Pitch
BK             Balks
BFP            Batters faced by Pitcher
GF             Games Finished
R              Runs Allowed
SH             Sacrifices by opposing batters
SF             Sacrifice flies by opposing batters
GIDP           Grounded into double plays by opposing batter

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2.players.csv

nameFirst      Player's first name
nameLast       Player's last name
nameGiven      Player's given name (typically first and middle)
playerID       Player ID code
yearID         Year
stint          player's stint (order of appearances within a season)
teamID         Team
lgID           League
G              Games
AB             At Bats
R              Runs
H              Hits
2B             Doubles
3B             Triples
HR             Homeruns
RBI            Runs Batted In
SB             Stolen Bases
CS             Caught Stealing
BB             Base on Balls
SO             Strikeouts
IBB            Intentional walks
HBP            Hit by pitch
SH             Sacrifice hits
SF             Sacrifice flies
GIDP           Grounded into double plays
salary         Salary

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3.teams.csv

yearID         Year
lgID           League
teamID         Team
franchID       Franchise (links to TeamsFranchise table)
franchName     Franchise name
divID          Team's division
Rank           Position in final standings
G              Games played
GHome          Games played at home
W              Wins
L              Losses
DivWin         Division Winner (Y or N)
WCWin          Wild Card Winner (Y or N)
LgWin          League Champion(Y or N)
WSWin          World Series Winner (Y or N)
R              Runs scored
AB             At bats
H              Hits by batters
2B             Doubles
3B             Triples
HR             Homeruns by batters
BB             Walks by batters
SO             Strikeouts by batters
SB             Stolen bases
CS             Caught stealing
HBP            Batters hit by pitch
SF             Sacrifice flies
RA             Opponents runs scored
ER             Earned runs allowed
ERA            Earned run average
CG             Complete games
SHO            Shutouts
SV             Saves
IPOuts         Outs Pitched (innings pitched x 3)
HA             Hits allowed
HRA            Homeruns allowed
BBA            Walks allowed
SOA            Strikeouts by pitchers
E              Errors
DP             Double Plays
FP             Fielding  percentage
name           Team's full name
park           Name of team's home ballpark
attendance     Home attendance total
BPF            Three-year park factor for batters
PPF            Three-year park factor for pitchers
teamIDBR       Team ID used by Baseball Reference website
teamIDlahman45 Team ID used in Lahman database version 4.5
teamIDretro    Team ID used by Retrosheet