Thursday, April 23, 2009
It is good to get away
Posted by Jonathan Halket at 1:06amOn average, teams play better at home than away. Home teams won 54.26 percent of the time in 2007 (all stats here will be from 2007). Teams play better at home because their players play better at home (duh). But does playing better at home translate into better fantasy performance at home? When it comes to hitters, the answer is a (rather) unqualified yes. However, for pitchers, things are not as clear.
Home batters score 5 percent more runs and hit 5 percent more home runs. I'll assume that means that typical fantasy hitters score more at home than away.
Of course, away pitchers get scored on more too. So, why might away pitcher fare better in your fantasy league than they do in real baseball? There are two crucial reasons. First, fantasy pitchers are mostly comprised of starters and closers, and wins and saves are scoring stats. Second, batting first in any inning gives away starters and closers a better chance to score in those stats.
When I am at a Mets game, I could care less who gets the win or whether there was a save opportunity as long as the Mets win the game. When I am watching a game for fantasy purposes, once my starter can't get a decision, I couldn't care less which team wins the game.
It is easy to see why being away gives a starting pitcher a better shot at winning (everything else equal - which I will come back to in a bit). Let's say that the your starter is going to pitch only six innings. Being away gives his team seven turns at bat to take the lead while he can still figure in the decision.
Similar reasoning works for closers and saves. The home team gets "last licks"—the away team cannot win with the last at-bat. So, if the home team is trailing going into the ninth inning, then there is no save opportunity that day for the home team; home teams cannot get saves in extra innings. The home team only has eight chances to take a lead in order to give the closer an opportunity for a save, while the away team has at least nine (of course, the away team also has more chances to take a lead so large that there is no save opportunity).
What do the numbers say?
Home SP win%: 35.28
Home SP lose%: 33.61%
Away SP win%: 33.36%
Away SP lose%: 37.60%
Away SP win/decision: .4701
Home SP win/decision: .5160
Home save%: 24.31%
Away save%: 24.93%
Home save% (as % of home team wins): 44.80%
Away save% (as % of away team wins): 54.50%
The numbers tell us that starting pitchers are more likely to win at home than away and have a higher winning percentage (wins/(wins+losses)) at home. However, the difference isn't nearly as big as difference in the teams' probabilities of winning. A home team is about 19 percent more likely to win than an away team ((.5426-.4574)/.4574 = .186), but a home starting pitcher is only about 6 percent more likely to win ((.3528-.3336)/.3336 = .0575). So the extra offensive chance helps the away starting pitcher quite a bit.
For closers, the effect is much stronger: away closers are slightly more likely to get a save than home closers. (One note: I've counted any game where a team gets a save as a save for the "closer." Data-wise, this simplified things a lot).
To summarize: the home-away advantage for starting pitchers is smaller than the advantage for the home team, but still positive. When it comes to closers, though, don't bother worrying about on which side of the infield the closer's dugout lies.
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Very interesting stuff, Jonathan. Nice work.