Boston Red Sox David Ortiz at Yankee Stadium in New York

Ask anyone about the playoff prospects of the 2010 Red Sox and they are sure to tell you that a large part of them are riding on the bat of a resurgent David Ortiz.

Papi has been one of the biggest cogs in the Red Sox machine for the better part of the past decade. Pushing the team to the brink of a World Series appearance in 2003, he lit worlds on fire bringing the club to two world championships in 2004 and 2007.

Then 2008 struck. Downed by an injury to his left wrist, Papi missed 45 games in June and July recovering from his subsequent surgery. Since then, Ortiz hasn’t the same.

Wrist injuries are death on power hitters. They decrease bat control and bat speed – two of the most important components of power hitting.

But, the wrist is just one development in the evolution of David Ortiz as a hitter. He turned 34 this past November, showing signs of aging in his last few seasons. There were PED allegations. And, it wasn’t long before the injury that Ortiz was struggling at the plate, leading to suspicions that Ortiz has become somewhat of a second-half hitter.

Still, what seems to have happened to Ortiz is that his wrist has combined with some of the drawbacks of aging – suggesting that Ortiz’s bat speed has slowed. For many who watched Ortiz hit in 2009 – especially in the early months of the season – he had lots of trouble making solid contact, especially when attempting to catch up with fastballs. Though his bat came around later in the year, particularly after the all-star break – where he posted a .258/.340/.516 line, with 16 home runs in 248 at-bats – it doesn’t mean that he’s out of the woods. There are a lot of signs that this extended run is more than just a slump or injury that can be recovered from asOrtiz is beginning to follow many of the classic signs of aging for a big, left-handed slugger.

The first point of concern is his dropping contact rate. After highs of 80.1 percent and 79.5 percent in ’07 and ’08, his rates dropped considerably to 76.7 percent in ’09. The sudden drop from ’08 to ’09 is the truly concerning point, as it suggests exactly what we’ve seen with our eyes and what would be indicated by problems with a wrist – decreased bat speed and bat control. Still, the ’09 number is not far below his rates in ’03 (77.4 percent) and ’06 (77.9 percent), so there is some hope that it was just a bad year. But, given the rest of the body of evidence, don’t bet on any significant recovery.

Keeping with the theme of Ortiz’s swinging habits, his increased O-Swing percentage is another worrisome indicator of his batting skills. An even clearer trend that his declining contact percentage is the rate at which he has been swinging outside of the zone. In every season since 2004, Ortiz has steadily increased the percentage of pitches he offers at outside the zone.

While hacking at bad pitches is always a bad thing, the fact that it has risen so abruptly in the last two seasons (18.5 percent O-Swing in 2007 versus 22.1 percent in 2009) is particularly troubling. When hitters are suffering from decreased bat speed and struggling with fastballs, they must begin their swing sooner in order to catch up with these pitches. While this helps them catch up to fastballs, it can have the negative effect of hurting their ability to correctly diagnose pitches. This can affect their ability to hit off-speed offerings, especially those that follow a similar plane as the fastball they are gearing up for.

To visualize this, think of Barry Zito’s loopy curveball versus Francisco Rodriguez’s hard curve. Zito sacrifices some of the deception in his pitch for increased movement. With a large difference in the trajectory of his curveball versus his fastball, it can be diagnosed early by hitters. On the other hand, K-Rod throws a hard curve with less movement, but a closer trajectory to the fastball – and thus more deception as it takes longer for this difference in trajectory to be recognized by a hitter.

When hitters like Ortiz are speeding up the timing of their swing, they are sacrificing time that would normally be used to recognize certain off-speed pitches, thus hurting their ability to hit these off-speed pitches, resulting in less contact made and more swings at off-speed pitches outside the zone.

In addition to his struggles with his pitch selection and making contact, Ortiz is also struggling with his ability to hit for power. Since 2006, Ortiz has seen a decrease in his rate of home runs per fly balls, which topped out at 26.1 percent in ’06, declining steadily through last season, where it bottomed out at 13.4 percent.

This power outage also points to diminished bat speed which has manifested in two ways: one, in more opposite-field fly balls (and more fly balls in general), and second, in fewer home runs, as a result of less energy being imparted on the baseball via less bat speed, which is compounded by even less energy imparted on the ball when contact is made in the direction of the opposite field, when the bat is not yet at maximum velocity. It’s a vicious cycle.

At this point in his career, Ortiz is becoming somewhat of a liability to the team. Still, there are reasons to be hopeful of a recovery of some part of his former glory. His vastly improved second-half, where he posted a .258/.350/.516 line gives some real reason for optimism that he can outperform his poor .794 OPS and abysmal 0.7 WAR on the year. In addition, his very low .266 BABIP is a reasonable bet to turn around – though, the optimism should be tempered somewhat, as he has posted two consecutive seasons of sub-par BABIPs (.273 BABIP in ’08 and .266 in ’09).

If his ’09 BABIP had registered near his career average of .304, his batting average would finished in the low-.260s with an OPS of about .860 – just about a dead heat with his ’08 production. Still, though Ortiz’s overall line improved between the first and second halves of ’09, his BABIP did not – at just .261 before the break, versus .272 after.

While it is certainly clear that David Ortiz is not the same hitter he was between ’03-’07, it is very difficult to say whether or not he will continue his slide or be able to post a repeat of ’08. The addition of 1.0-1.5 WAR would be a huge boost for the team, and a .260/.850 line is not at all out of reach, especially when considering Ortiz’s resurgent second-half. Bill James’ echoes this sentiment, projecting a .264/.877 season.

But the true value of Ortiz’s abilities may lie in the eye of the beholder. Running a few quick projections, inputting Ortiz’s .794 OPS as his baseline ability yields a projected OPS of .816 for 2010. Assuming that his .866 OPS is his baseline ability yields an estimated 2010 OPS of .848. Though a step up from his 2009 line, they, too, suggest that Ortiz’s days as a premier designated hitter are likely in the past. The continued aging of the big-bodied slugger seems to have put another dent in his bat, which may prove too much for him to overcome.

If anything, Ortiz must be paired with a right-handed platoon mate. This would have a two-fold benefit of, one, improving the production out of the middle of the order, where Ortiz batted just .212/.298/.418 against southpaws. Second, the additional days off would serve to keep Ortiz’s wrist and legs fresh throughout the season, decreasing his injury risk and keeping him healthy for the postseason.

With just a zero-dollar buyout, $12.5 million club option due for Ortiz in 2011, it is looking more and more likely that 2010 will be Ortiz’s last in a Boston uniform. Barring a huge – and unlikely – resurgence this upcoming season, it is very difficult to imagine the designated hitter being worth his $12.5 million option. It’s too bad he’s meant so much to this team for so long – it will be tough to see him go.