What happened to Jon Lester?

Philadelphia, PA (Sports Network) - And you thought Tim Lincecum and Heath Bell were the only pitchers to have their careers jump off a cliff this season?

Boston starter Jon Lester is right there with them, especially after last night's disaster against the Chicago White Sox.

Don't tell the White Sox that the fourth of July ended two weeks ago. With the fireworks display they put on at Fenway Park on Tuesday, it's clear they're still celebrating.

The first place Chi Sox blasted four extra base hits against Lester with the grand finale coming on a massive Kevin Youkilis bomb over the Green Monster in left (I wonder what Bobby Valentine was thinking as Youk rounded the bases). Lester exited the game after giving up seven total hits and six runs in four excruciating innings of baseball.

If Lincecum's nickname is "The Freak" then Jon Lester's should be "The Underachiever." It may not roll off the tongue, but at least it's accurate.

Coming into this season, Lester was seventh among American League starting pitchers on our site's fantasy rankings. Today, he's at No. 57. And remember, that's just the American League. If you include NL starters, his ranking falls to 121st.

Lester isn't in total free-fall mode yet, but he's getting closer. In three July starts, his ERA rests at 6.60, his worst since posting a 7.66 ERA in August of 2006 (unless you count March of 2008, when he allowed four runs in four innings pitched in his only start).

From 2008-2010, Lester (5-7, 4.80 ERA) finished in the top 10 in ERA in the American League every year. This season, he's 32nd in the league in that statistic.

The other day in a text message conversation, my friend made a good point that Lester is pitching more like a fourth or fifth starter this year than an ace.

It's hard to argue with him. After leading the Red Sox with 15 wins last season, Lester is tied with Josh Beckett and Daniel Bard (who was demoted to Triple-A more than a month ago) for third on the team with just five wins in 19 starts.

The 19 starts could be part of Lester's problem. Part of Lester's brilliance over the past few seasons has been his ability to stay healthy. Since 2008, the 28-year-old has pitched 930 and 2/3 innings. While he's not quite approaching Justin Verlander (1,057 innings) or CC Sabathia (1,071 innings) territory, that's still a lot of innings.

Earlier in the season, I theorized that Lincecum's woes could be a product of how many innings he's thrown over the last five seasons (he's pitched 986 and 1/3 since 2008) and I think Lester's struggles could be linked to overuse as well.

A good way to measure the wear and tear on a pitcher is by looking for a drop off in velocity. While Lincecum's drop in velocity has been well- documented, Lester's regression hasn't been quite as evident.

His average fastball this season has been thrown at 92.2 mph, only a 1.3 mph drop off from 2010 when the two-time All-Star averaged a career-high 93.5 mph on his heaters. Last season, Lester threw only 92.6 mph while still putting together a pretty good year (15-9, 3.47), so perhaps the speed of his pitches isn't Lester's biggest issue (though Youkilis did smack his 93-mph offering about 400 feet Tuesday night).

Here's what I think might be causing Lester the most trouble. For whatever reason, he has thrown an inordinate amount of sinkers this season. Lester only started throwing the pitch in 2010 and even last year, he was only using the sinker on 16.7 percent of his pitches. This season that number has risen to 29.4 percent.

I'm not exactly sure why halfway through his career Lester is deciding to abandon his four-seamer (a pitch he used to throw on almost 65 percent of his pitches but now throws only about 31 percent of the time) in favor of a sinker, but it's a pretty dramatic change in approach. When Lester relied heavily on his fastball early on in his career, he was one of the league's premier strikeout pitchers. Now he's pitching to contact and the results haven't been pretty. Opponents are hitting .282 against Lester in 2012 compared to .249 for his career.

Even lefties are starting to see the ball better against Lester. They're mashing .270 against this suddenly sinker-infatuated version of Lester, 29 percentage points higher than they have in previous seasons. Lester's new approach has also rendered him less useful in the strikeout department. Currently, he's on pace to finish with 174 strikeouts, his fewest since 2008.

Whether it's wear and tear, a lack of confidence in his fastball or whether he's just exhausted from being a part of Boston's tumultuous clubhouse, Lester hasn't been the same pitcher in 2012 than we've seen in the past. He's still owned in 93 percent of Yahoo leagues, so he hasn't completely shattered everyone's confidence yet but I'm doubtful that Lester will be able to return to the form that made him an All-Star in 2010 and 2011. Lester's resume says "ace" but his stats this year tell a much different story. Proceed cautiously with the veteran lefthander.

Comments? Criticism? Applause? Contact Jesse Pantuosco at jpantuosco@sportsnetwork.com.