C     Catcher
1B     1st baseman
2B     2nd baseman    
3B     3rd baseman
SS     Shortstop
LF     Left Fielder
CF     Center Fielder
RF     Right Fielder
DH     Designated hitter
Sub     Substitute
INA     Inactive
OF     Outfielder
Pitchers:
Ace     Your Top pitcher
SP      Starting pitcher
SP2     Starting pitcher 2nd in rotation
SP3     Starting pitcher 3rd in rotation
SP4     Starting pitcher 4th in rotation
SP5     Starting pitcher 5th in rotation
Long     Long reliever
RP1     Relief Pitcher 1
RP2     Relief Pitcher 2
SM      Setup Man
CL      Closer
MR     Middle relief
SR      Short relief