THE BOOK--Playing The Percentages In Baseball

Wednesday, March 17, 2010

Why I can’t stand the “one run games” as a category

This has bothered me to no end.  I’ll try to explain why in my way, which won’t be any good.  And then I’ll link to a great explanation.  For one thing, the home team can get 0 to 3 less outs per game to score than the visiting team. Secondly, what is a close game all game can get undone by a never-ending ninth inning.  So, while the teams may have been strategizing as small-ball for 8 innings, makes it look like a blowout.  The “one-run game” is an AFTER-THE-FACT categorization of the game, but we use the category to describe it in real-time or before-the-fact scenarios.  A much better way to categorize a game as close is to use win expectancy and leverage index.  The closer the win expectancy is to .500 for one team, and the higher the LI, then the closer the game.  There.  That’s what we want.

Here’s Hawerchuk on the NHL:

In the last 90 seconds of a one- or two-goal hockey game, the trailing team gets much more value out of scoring a goal than they do out of preventing one.  Hence the strategy of pulling the goalie.  The net result is that lots of one-goal games become two-goal games, and lots of two-goal games become three-goal games.
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We can remove the effects of pulling the goalie by looking at the score before the last two minutes of the third period:

Prior to 18:00 No ENG ENG
1-goal 33.3 32.5 24.3
2-goals 21.7 20.6 22.5
3-goals 12.2 11.9 17.9

ENG = empty net goals

It turns out to be a very minor difference.  But fundamentally, there are a lot more one-goal games and a lot fewer three-goal games than we’d think based on the score at the end of regulation.