Slugging percentage is, of course, a "power" stat. It's got the word slug right there in the middle of it, and also the word lug, and the word gin, all powerful things. But then Mike Trout comes around and slugs .564, and of course Trout has a ton of power but have you ever wondered just how much of Mike Trout's slugging percentage comes specifically from his speed? There's the doubles he turns to triples, of course. And the singles he turns into doubles. The infield hits he beats out. But there's also what defenders have to do to defend him; third baseman have to play closer than they want to, middle infielders have to bunch in a little, it's even possible (somebody should check!) that pitchers are more likely to work him up in the zone than a similar power hitter, knowing that inducing a groundball doesn't have quite the rate of return that it would have against an Adam Dunn-type .564 slugger. There's also the bigger gaps he gets because outfielders squeeze in just a little bit on him, knowing that otherwise he hits a routine single and turns it into a double. The full extent of it is impossible to measure. But if I had to guess, I'd guess that Mike Trout gains 35 extra bases a year based on his speed. That, if he ran like Josh Willingham runs, he'd have slugged .501 last year. What do you think, Shin-Soo Choo?
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I'm not sure if I can post a link here, but here's a gif of the Bonifacio play: