Like most Angels' fans, I'm concerned about the health of the Halo pitching staff.  While poking around with some Pitch fx data, I tried to use that information to try and shed some light on possible reasons this staff is having problems staying healthy.  While I'm far from an expert on the physics of throwing a baseball or how different pitches effect different muscles, I used some common sense in formulating my conclusions.  Here's my thoughts, please correct me if I go off the mark:

• Fastballs and change-ups put the least amount of stress on a pitchers arm;
• Throwing a slider puts the most strain on a pitcher's arm, especially their elbow based on the required "snap" a pitcher must put on the pitch to make it break and the velocity the pitch is thrown;
• A cutter will put more strain on a pitchers forearm than his elbow based on how the pitch is thrown.  I'm assuming a cutter is thrown like a fastball, but the pitcher uses his wrist to create spin;
• I have no idea what effect a curveball has on a pitchers arm or shoulder.

Within the data below, I've included some outcomes from each type of pitch thrown.  With this data I make the following assumptions:

• A "swing and a miss" strike is the best outcome for a pitcher.  The pitch was good enough for the hitter to swing, but was unhittable;
• A called strike either fooled the hitter or the hitter realized he was unable to hit the pitch;
• A foul ball or foul tip are the next best outcomes since the hitter was able to make contact, but was unable to do anything with it;
• Contact is when the hitter was able to put the bat on the ball in fair territory for either a hit or out.  The least valuable outcome.

Here's the pitch fx data for each of the Angels' starters from 2008 and how it relates to the above thinking.  I'm going to make conclusion based on the effect of each pitch and not how each pitch relates to each other.  For example, how an inside fastball will set-up a curve.  The better the first pitch, the better the second pitch will look.  Obviously, thrown in different situations, the pitches don't have the same effect.
(note:  If you look closely at the raw data, you'll notice some numbers don't jive with each player's season total; hits allowed, home runs allowed, etc.  I emailed Josh Kalk, who created the pitch/fx tool, and he stated, " PITCH f/x missed some pitches during the season and the tool wasn't updated with the last month of games so that is the reason for the difference.")

John Lackey (1883 pitches thrown)

Lackey is currently scheduled to open the season on the disabled list due to a forearm strain.  Based on the first set of assumptions above, could we assume that Lackey's forearm problems are a result of the frequency he throws his cutter?  Based on the pitch fx data, the cutter is his worst pitch.  Lackey's cutter has the lowest swing-and-miss rate and the highest contract%.  It causes me to ask, why does he throw it so often?  With this data, it looks like Lackey's best pitch is his curve.  Would he be more effective throwing his curve in some situations rather than the cutter?  And stay healthier?

Ervin Santana (3325 pitches thrown)

I can see why Santana throws so many sliders, it's a great pitch.  He has a high swing-and-miss rate with it, and hitters have a hard time making contact.  But he puts so much strain on his elbow throwing the pitch, it's understandable why he's having health issues this spring.  If he's able to pitch this season, what type of pitcher will he be?  Will he be afraid to thrown his most effective pitch in order to save his elbow?  And finally, if he does thrown it, will it still be as effective?

Joe Saunders (3164 pitches thrown)

Joe Saunders has been one of the most durable pitchers on the Angels staff.  Except for some shoulder tightness this spring, he hasn't had a significant injury or spent any time on the disabled list (thanks to this site for the information).  This could be due to his throwing the least stress inducing pitches about 57% of the time.  Saunders is also the starter on the Angels' staff who throws more to contact than over-powering hitters (he has the highest contact% of the four pitchers studied).  When looking at this data, I wondered why Saunders doesn't throw his curveball more often.  It has the lowest contact%, a good swing-and-miss rate, and is rarely fouled off.  I would think mixing in a pitch that looks this effective would create better results.  One thing not shown here is a pitch's speed and movement.  I had noticed Saunders' fastball was clocked a little faster and with more movement than Lackey's, but Lackey seems to have better results (21.1% vs 18.3% contact%).  Saunders throws his fastball more often and appears to lack the command of the pitch that Lackey does, but unless he's using the fastball to set-up his other pitches, a little improvement / command of his fastball and a better mix of pitches may allow Saunders to take his game to the next level.

Jered Weaver (3167 pitches thrown)

I like Jered Weaver.  He throws his slider a little too often which may result in an added risk of injury, but of the four pitchers, he throws it with the least velocity.  Over the course of his career this may reduce the chances of injury to his elbow since he's putting a little less stress on it.  The one knock on Weaver is his lack of an "out pitch".  In the recent chat with LA Times sportswriter Mike DiGiovanna, when asked about Weaver, he stated "I think he is going to be a solid No. 3 or 4 starter, but his lack of a put-away pitch will prevent him from being an ace. You can see it when he gets to two strikes. Look at how many foul balls there are. He doesn't have a nasty strikeout pitch."  Weaver's change-up looks like a good pitch as he gets plenty of swing-and-miss strikes with it (the highest rate among all pitchers), however hitters are able to foul off his fastball (also the highest rate among all pitchers).  Maybe a better mix would improve Weaver's results. 

Here's some summary data comparing each pitcher.  The swing strike data is swing-and-miss and foul balls combined:

The depth at which pitchers use their pitches is so much deeper than what I've touched on here.  Good pitchers (and catchers for that matter) usually are thinking two or three pitches ahead in order to set-up the hitter.  I've only looked at this data on a pitch-by-pitch level looking for clues as to why the Angels' pitchers are getting injured and why they are getting the game results that they are. 

I've asked quite a few questions without providing any definite answers (sorry about that), but I thought this information was interesting and would at least spark some good discussion.