Nolan Arenado, Ball Magnet

This morning I was scrolling through baseball stats at the mlb.com mobile site, and I noticed something curious. This is the list of major league leaders for assists: 

Rk		Tm	G	Inn	A ▾	Pos Summary
1	Troy Tulowitzki	COL	27	234.0	101	SS
2	Aaron Hill	ARI	29	260.0	92	2B
3	Starlin Castro	CHC	26	230.0	91	SS
4	Alexei Ramirez	CHW	29	260.0	90	SS
5	Brian Dozier	MIN	26	238.2	87	2B
6	Jimmy Rollins	PHI	24	204.1	87	SS
7	Nolan Arenado	COL	30	267.0	83	3B
8	Marcus Semien	CHW	29	251.0	83	2B-3B
9	Jose Altuve	HOU	28	249.1	81	2B
10	Ben Zobrist	TBR	30	237.2	80	2B-OF-SS

Provided by Baseball-Reference.com: View Original Table
Generated 5/2/2014.

Tulo, Hill, Castro, Ramirez, Dozier...all make sense. They're middle infielders, and middle infielders get a lot of ground balls. But there's the Rockies' Nolan Arenado tied for seventh. He's a third baseman. That seems out of place.

Arenado is in just his second year, but he's already won plaudits for his glovework. He won the National League Gold Glove last year as a rookie, and he hasn't let up this year. Still, how unusual is it for a third baseman to rank in the top ten in assists?

Really unusual, it turns out. As in, it hasn't happened since baseball expanded in 1961. The only third basemen in the 53 seasons since then to have finished in the top 20 in major league assists were Brooks Robinson (No. 13 in 1967), Ron Santo (No. 15 in 1967, No. 20 in 1966), Brandon Inge (No. 19 in 2006), Clete Boyer (No. 19 in 1962, No. 20 in 1961), and Graig Nettles (No. 20 in 1971). Nobody's been close to the top 10 until now.

Is this a fluke? I figure there are three things that could give Arenado a big advantage. First, handedness. Right-handed batters hit grounders to the left side of the infield more than left-handed batters, and managers load up on right-handed batters in order to gain a platoon advantage when they face lefties. Do the Rockies feature an unusual number of southpaw pitchers, resulting in opposing lineups full of right-handed batters, hitting grounder after grounder to third?

This year, lefties have pitched 37% of Colorado's innings. That's a lot. But it's not extreme: The Rangers, White Sox, Angels, Rays, Phillies, and A's all have had a greater proportion of innings pitched by lefties. So Arenado's pace isn't because he plays behind a steady stream of left-handed pitchers. 

How about the pitchers' tendencies themselves? Do Rockies pitchers, in an effort to keep batted balls out of the thin air at Coors Field, generate tons of ground balls? 

Again, yes, but it's not dramatic. Rockies pitchers have induced grounders on just under 49% of balls in play. That's high, but not highest: The Pirates, Phillies, Giants, and Dodgers have all gotten more. So that's not the explanation.

Finally, how about games played? Have the Rockies played more games than others, giving Arenado a chance to see more balls hit his way? Again, kind of yes. The Rockies have played 30 games so far, second-most in the majors. But other than the Tigers, every team's played at least 26. Maybe when the games even out, two of the players below him on the list above, Marcus Semien and Jose Altuve, will pass him. But that's probably it, at least on that basis. (And no, Arenado's assists aren't inflated by shifting, because, as Rockies Zingers points out, the Rockies do relatively little shifting.)

More likely, he just slows down. When a player's on pace early in the season to do something that's never been done before, the easy answer is to assume that he won't do it, either. But for a while here, I'm going to keep track of Arenado's assists and see if he can keep hanging with the middle infielders.