Chad Billingsley has been ridden hard this year. He is second in the National League with 61 innings pitched (behind Jake Peavy) and leads all of MLB in pitches thrown with 991. As you can probably guess, he's also thrown the most pitches per start. Here's the leaders in the National League:

Obviously Bruce Bochy doesn't care much for preserving his starters, with three Giants in the top six. Last year Lincecum and Cain were in the top 10 as well. But Billingsley still stands squarely above the pack. There are some AL pitchers that are closer than Peavy (due to not having to be pinch hit for) but Chad is even above them. The problem with this is that over time pitchers arms can wear down if they are overused. Pitchers that have been abused in recent years often end up on the DL with arm injuries or are just generally ineffective.

Another way to measure how much a pitcher abuse is through pitcher abuse points (PAP), a statistic developed by Joe Sheehan of Baseball Prospectus. PAP's work based on the theory that pitching doesn't hurt your arm, pitching while tired hurts your arm. Because of this, any start that lasts less than 100 pitches doesn't accrue any PAP's. Once a start lasts longer than 100 pitches, a pitcher starts to accrue PAP's at an increasingly high rate. For pitches 101-110, only one PAP is accrued for each pitch. But by the time you get to 120 pitches, 3 PAP's are added for each pitch thrown. Here's the full chart:

Based on this statistic, going from 130 and 135 pitches puts the same amount of stress on a pitcher's arm same as going from  100 and 115 pitches. This shows how much extra risk can be put on a players arm from just a few extra pitches if they go really deep into a start. So, here are the NL leaders in 2009:

Before you flip out and think that Chad's arm is falling off, the number of pitcher abuse points are calculated differently on Baseball Prospectus' Statistics Report. The exact formula can be found here. Even with this formula the results are still the same so there's not too much of a difference other than that the numbers are much higher.

You can see that some of Chad's high pitch counts have added up this year. He's pitched incredibly well so Joe Torre hasn't had a lot of reason to take him out, but he's still being worked harder than lots of other top pitchers have been. Last year Chad was ranked 34th in the majors with 23,023 PAP's. This makes his 2009 a bit concerning because he already has more PAP's than last year in only nine starts. Eric Stults is on the list too but it is entirely because of his 123 pitch shutout against the Giants. Other than that start he has not gone past the 100 pitch mark and he is averaging only 94.1 pitches per start.

Here's the qualifying players with at least an average of 2600 PAP"s per start in either 2006 or 2007:

I don't think there is any question that most of these pitchers have had troubles since these high risk seasons ocurred. Livan Hernandez is a difficult case because he was known for his durability but his FIP (fielding independent pitching) fell from 4.85 in 2006 to 5.77 in 2007. Carlos Zambrano lost over a strikeout per 9 innings after each of his abusive years and has made a trip to the DL the last two years, including his concering shoulder strain in 2008. He has has had notable drops in his release point, a sign of injury. Aaron Harang was fine for one more year before he had the worst FIP of his career in 2008. Daisuke Matsuzaka was good in 2008 before having a FIP over 10 and going on the DL with a shoulder injury this year. Dontrelle WIllis completely fell off the map with rising ERA's and injury issues. He recently made his season debut with the Tigers after a year in the minors. We all know about Jason Schmidt's struggles, he's only pitched 25.2 innings in 3 years with the Dodgers since his high-risk season. Bronson Arroyo has seen his ERA increase every year since 2006 including an ugly 6.56 mark so far this year.John Smoltz was great in 2007 but has pitched a grand total of 28 innings since then. Barry Zito joined the Giants after 2006 and hasn't had an ERA below 4 or thrown 200 innings in his two full years with the team.

A.J. Burnett, Roy Halladay, and Matt Cain are the only players on the list who have been mostly unaffected by their overuse but there are still some signs that do not portend future success. Burnett has the highest FIP (minimum 40 innings) of his career this year, with his lowest K/9 since 2001 and highest BB/9 since 2000. Matt Cain has the lowest K/9 rate, highest BB/9 rate, and highest FIP (by almost a full run) of his career this year. He's also lost nearly a mile per hour on his fastball. These are bad signs for a 24 year old, and probably could have been prevented if he hadn't been worked so hard at such a young age. Halladay may just be a freak, he really has been as good as ever this year. He has been in the top 5 in PAP's in the last two years so it could be that we will see some signs of injury in the near future. 

I didn't include 2008 because we haven't seen the results of the pitchers overuse yet. But the two pitchers who would have qualified were CC Sabathia and Tim Lincecum. Lincecum actually had 5289 PAP's per start last year. That is an incredibly high figure, no one has reached 5000 PAP's per start since 2004(when 4 players did it, including Jason Schmidt with an astounding 8558 per start! Maybe we should have seen the injury woes coming...). This raised eyebrows around the league (to say the least) as there was no reason to work such a precious young arm so hard for a non-contending team. The Giants could end up feeling the effects of the overwork of their young arms for years in a situation that was totally preventable.

So where does this leave Chad? First of all, there's no reason to panic right now It's not as if he's been overused for a number of years, it's only been a couple of months. There's still three-quarters of a season left and if it becomes clearer that the Dodgers will win the division then Torre could ease up on the gas pedal and let Chad get some more rest. But if Torre continues to work Chad hard this whole year and perhaps even longer then this could end up damaging his arm and severely hurting the Dodgers in the long term. He is currently on pace for 88,685 PAP's if he were to make 33 starts, just below the players on the above list who have been negatively effected the last few years. I think if he can just lower the pitch count a little bit, to say 105 pitches per start, he would be in a comfortable range of pitchers who are worked hard because of their effectiveness but yet aren't overused to the point of injury. It may be hard for Torre to remove him from games because he is so good but it would be a wise long term decision even if it costs the Dodgers a game or two in the process. Whatever happens, it will be something to follow over the course of the year because the health of our ace is at stake.