Sunday, January 06, 2008

And old "icing the kicker" study

"Icing the kicker" is the tactic of calling a timeout just before the opposition is about to attempt a crucial field goal. The idea is that the interruption upsets the rhythm and mental balance of the kicker, who now as an extra couple of minutes in which to envision screwing it up.

Does the strategy work? In 2004, Scott Berry and Craig Wood decided to check. They published their article in
Chance magazine, which I don't have – but Ivars Peterson summarized the study in an online column.

Barry and Wood looked at all "pressure kicks" (which would give the team a lead or tie with less than three minutes to go) in 2002 and 2003, normalizing them for weather, distance, and so forth. They found that icing the kicker did, in fact, work – reducing the chance of a successful kick from 76% down to 66%.

They say "the evidence is not overwhelming, but it is compelling."

The difference of 10 percentage points looks like a big effect, except that there were only 38 "icing" kicks overall. 29 of those kicks "should have" succeeded, but only 25 did. It's hard to believe that difference of only four kicks would be statistically significant.

Actually, the standard deviation for those 38 kicks is about 2.6 (the square root of 76% times (100 – 76)% times 38), so four kicks is only about 1.5 standard deviations away from expected. That's definitely not significant.

In fairness, the authors, who are statisticians, probably mentioned that in their article.

P.S. After writing this post, I found this, which points to more data from Stats, Inc. So I guess this is old news, but I wrote it, so I'm going to post it anyway.

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At Wednesday, January 09, 2008 1:26:00 PM, Anonymous Anonymous said...

I'm not even convinced that the data presented represents "icing" accurately. If a team really called time out with three minutes left, it's probably because the clock was running and they wanted to leave as much time left as possible for their own potential game-winning drive. I can't recall a team ever wasting a time out for icing with anywhere near that much time remaining.

Also, I'd bet there's some bias in including those kicks with three minutes left (which almost certainly do not involve icing): They're probably shorter in distance (which Berry and Wood accounted for, but Stats Inc. did not) because you don't have those desperation 60-yard attempts on 1st down as time expires. Plus, it's possible that the increased pressure makes last-second kicks more difficult than last-minute kicks.

I think if you really want to measure any effects of icing, you'd have to limit your kicks to those within the last 10 seconds or so. And that would probably reduce your sample size too much to get any meaningful results.


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