"Clutch measures how well a player performed in high leverage situations. It’s calculated as such:
The WPA stands for "Win Probability Added" and it tells us how much each plate appearance by a batter increased or decreased his team's chance of winning. LI is leverage index. Games that are late and close with runners on have a higher leverage than normal.
pLI: A player’s average LI for all game events.
Play by play data does not exist for all years. That is necessary for this stat.
I looked at all seasons with 300+ PAs and a clutch of 2.5 or higher using the Baseball Reference Play Index. The 3.5 for Simmons means he added 3.5 more wins by hitting better in the clutch than if he had just had his usual numbers.
Simmons batted .381 that year with 36 HRs and a 157 RBIs. His OBP was .423 and his SLG was .708. Click here to see his 1930 splits Here is a sample
|2 outs, RISP||0.402||0.437||0.732||1.168|
|Late & Close||0.429||0.461||0.857||1.318|