Ervin Santana improved to 5-0 with the Angels’ 6-1 win over the A’s yesterday. Can he keep up this pace? Let’s take a look.

Santana pitched two outs into the seventh inning, giving up four hits, a walk, and an unearned run, striking out three on his way to his fifth win of the season, and bringing his ERA to 2.48 and WHIP to 0.97 (The other 5-game winner on the Angels, Joe Saunders, is pitching to the tune of a 2.08 ERA and 0.95 WHIP). While Santana has long been pegged for some sort of improvement as he matures, he is far outperforming most all projections for the year, and some caution may be urged before yet calling a breakout season.

The Hardball Times puts his xFIP at 4.12, way off from his actual ERA (xFIP estimates what a pitcher’s ERA should be, given his strikeout, walkout, and home run rates (for more on using this see Mike’s earlier post)). His strikeout rate is 7.0 so far, not so different from his 7.2 last year and 6.5 and 6.4 in the years before; while his ground ball rate is actually slightly lower than it has been in the past (a 35.9% compared to the previous three years’  35.6%, 38.4%, and 36.6%). On the flip side, his fly ball rate, according to Fangraphs, is a little higher than previous years (46.2% compared to 45.7%, 44.2%, and 44.4%).

The big differences seem to be in his walk rate, which at 2.2 is way down from his prevous 3.3, 3.2, and 3.1, and in his home run rate, which at 0.72 is another world from last year’s 1.49 (and yet, two years ago it was .96). Two more interesting points: One, THT puts his Defense Efficiency Ratio this year at .767, the best it has ever been for Santana, while his line drive percentage (which tends to inversely correlate to DER) is in line with his previous numbers (17.9% this year, 18.7%, 17.3%, 19.0% previously). Two, his BABIP thus far is .244, but in 2007 it was .333; in 2006, .269; 2005: .305.

Okay. We got a little thick in the numbers there. And granted, it may be too early to be sure about some of these states. But it’s hard to say if this year’s good start is impossible, given his history and capacity for development. Though his strikeout rate isn’t out of line from his skills, his walk rate likely is (I’m sure he could be improving, though probably not yet so dramatically), so that should be expected to regress a bit. His groundball, home run, and line drive rates aren’t impossible, given what he’s done before, and the DER and BABIP may be an indication that the Angels defense is playing better than normal when he’s on the mound, or simply that he’s benefiting from some (perhaps not unwarranted) good luck.

All in all, it seems possible that Santana may be looking at a season more in line with 2006, when he went 16-8 with a 4.28 ERA and 141 strikeouts. He might even do a bit better. But I don’t see any reason to assume his ERA will stay this low.