[This post was written by loyal Nation member, Warren Leeman, who is a regular commenter under the name Shchi Cossack. Thanks, Warren!]
The word “leverage” is a sabermetric measurement of how crucial the game situation is. High leverage situations occur when the game is close. Low leverage situations are those when the game is a blow out.
The most important way leverage enters into baseball strategy is bullpen usage. Even without statistical documentation, savvy individuals can recognize high leverage situations. Big league managers must recognize and deal with high leverage situations on almost a daily basis.
Based on comments attributed to Bryan Price and watching his bullpen management, high leverage consists of two situations: when opposing runners are on base with the tying or go-ahead runs, or the ninth inning with a 3-run lead or less.