Pat Burrell was just replaced as the DH in Tampa Bay and it's only a matter of time before the Mariners do something about their twin-DH issue out west if they plan on competing, but that does not mean every struggling designated hitter is going to stay that way. After an April that saw David Ortiz at a line of .143/.238/.286—a line so poor the Mets would have used him out of the two spot in the lineup—any kind of comeback resembling the one he had in 2009 seemed like a far-fetched dream.

Here we are halfway through May though, and Ortiz has managed to climb up from the depths all the way back to…well, replacement level. It's a start though, and while totally unrealistic, his .333/.370/.714 May is encouraging.

There are reasons to be both optimistic and skeptical of Ortiz going forward. Optimism springs from his .245 Isolated Power—it takes nearly a full season for ISO to stabilize, but given he was at .243 in 2008 and .224 in 2009, it's probably safe to assume the big guy can still drive the ball with authority. Skepticism springs from the fact that there are times where it seems the only thing Ortiz can do is drive the ball with authority—the rest of the time he misses the pitch by a mile.

Ortiz is striking out in 39 percent of his at-bats, which is 17 percentage points above his career rate and 14 percentage points above last year's rate. The 34-year old's bat is a bit slower than it used to be, but there is more to it than that. You can see exactly what is happening to Ortiz, especially if you are familiar with how he used to be at the plate.

Ortiz, like Barry Bonds before him, used to be very selective about exactly what he would swing at. He had a zone within the strike zone, and if a pitch traveled in the vicinity of it, it ended up in orbit. Ortiz would draw walks from this selectivity—pitchers would throw pitches in the strike zone, but were generally trying to avoid letting Ortiz get a hold of one, so they didn't necessarily challenge him consistently. Pitchers seem to be aware that they shouldn't throw the ball in that area either, as first-pitch strikes to Ortiz remain at a below-average rate as they have since 2004, even with him hitting .224/.294/.469 this season.

Ortiz still has this zone today. There is a cross-shaped area within the strike zone that Ortiz has a high success rate in, but if the pitch isn't there, he has issues with it. He swings at pitches he never would have gone for back in the day—specifically, inside pitches he thought he could turn on and pull. He doesn't have the bat speed for that though anymore, so instead he strikes out before the pitcher will throw him a pitch he can do something with. He also has a tendency to chase pitches high and low in the zone, but he has still managed to avoid chasing pitches away and outside. His walk rate has dropped from 16.6 to 14.3 to 11.8 to 9.2 percent since 2007, to give you a sense of what else changed besides his strikeout rate and batting average.

This chart from Inside Edge does a good job of showing what I've described above:

As R.J. Anderson demonstrated in a TMI piece earlier this year, this is not a 2010 trend for Ortiz—it started in 2009 (and was a problem) and has been even worse in 2010. One thing to take note of though, was that Ortiz had swung and missed on 44 percent of his swings back when that piece publiushed in mid-April. A month later, Ortiz is swinging and missing on 28 percent of his swings, which is still below the league average, but is also a vast improvement over his early season returns.

Ortiz has worked his way back to replacement level (his WARP is -0.2 as of today) thanks to a strong May, but let's remember what was said about Ortiz zone—if pitchers keep the ball out of that area and work him inside, high, low, or on the corners, Ortiz is not going to be able to succeed for long. Throwing the ball in that cross-shaped zone is a mistake, and Ortiz can still wail on those. If his May is any indication, plenty of pitchers are going to throw mistakes, and that may be enough to keep Ortiz' bat useful in 2010.