League adjustment (from the previous link):
The league adjustment is a small correction to make it so that each league’s runs above average balances out to zero. Each league’s Batting Runs + Base Running Runs + Fielding Runs + Positional Adjustment often total to something slightly different from zero. The league adjustment fixes this and has a very tiny impact on player value.
To find the league adjustment find the league specific values (AL or NL) and do the following:
League Adjustment = ((-1)*(lgBatting Runs + lgBase Running Runs + lgFielding Runs + lgPositional Adjustment) / lgPA)*PA
This will tell you how many extra runs you need to add to the entire league per PA and then you multiply that by the specific player’s PA. This will add between 0 and 5 runs to a player’s value per season based on their league and PA.