A hitter’s overall contribution on the bases. His basestealing, avoidance of the double play, and success at taking the extra base while avoiding being thrown out.
BR Gain (or Loss if a negative number) is the total of all the types of extra baserunning
advances minus the (triple) penalty for all the BR Outs compared with what would be
expected based on the MLB averages. Zero is average. Plus numbers are above average and negative numbers are below average.
SB Gain - Stolen Base attempts must be successful greater than about two thirds of the time to have a positive result on the number of runs scored.
For a summary of each runner, look at the far right column called "Net Gain". It combines BR Gain and SB Gain.