(With the MLB Draft about 9-10 days away, I thought I would weigh in on this topic.)
I am not trying to oversimplify this but here are some reasons that I can see that make pitching from the left side more valuable than right side.
First of all in the youth leagues players have very little experience hitting against LHP’ers. When kids take batting practice most do not have a lefty tossing at the hitter. Some hitters face a mental block when the ball is coming in from the “wrong side” of the mound.
As players move to older leagues they begin to see more and more lefthanders but they see far more right-handers during their seasons. So why do right handed hitters struggle against left-handed pitching?
• LHPs have considerable arm-side run (away from RHHs)
• Pitchers work away from hitters (especially against metal bats)
• RHHs are natural pull hitters
(The above is for MOST but not ALL lefties.)
Therefore RHHs are constantly trying to pull pitches off LHPs
Holding runners close to their bases is a huge component of pitching. If a pitcher is unable to hold runners effectively, it gives the opposing team a considerable advantage. While RHPs might be at a slight edge at holding runners at second base, LHPs should benefit greatly at holding runners at first base.
The LHP is staring directly at the runner at first so he is able to see any subtle changes in the runner’s lead. Some LHPs have an innate ability to read runners as they attempt to steal second base. If they are able to do this, they can pick over immediately and get an easy out. Other LHPs cannot do this, but if taught properly can develop a pick-off
move that is devastating which can get one or two outs per game. Not only do LHPs have an opportunity to get easy outs at first, but by limiting a runner’s lead at first base he gives his fielders an extra step in turning a double play or reduces the chance of the runner taking an extra base after the ball is hit.
Another reason that LHPs are important is that they give your staff balance. The old cliché of pitching is to keep the hitters off-balance. That not only applies to the pitches a hitter sees from a pitcher, but also the various looks you give a hitter during a three game series.
Even though you may start three different types of guys in your weekend set, if they are all RHPs, it gives the hitter some sense of familiarity. However, if you are able to mix in one LHP or even two LHPs as your starters, you are already forcing the hitter to make an adjustment before the game starts.
Bullpen balance is equally important for your overall staff success. Having one or more LHPs in your pen gives you options in the late innings when games are decided. A large number of teams have big time hitters that swing from the left side and if your team does not have LHPs to neutralize those quality bats it could cause trouble late in games. Remember teams offensively try to create balance as well and if they know that your team doesn’t have lefties in your bullpen they are able to stack their lineup with LHHs with no fear of match up problems at the end of the game.
LHPs also hold a distinct advantage against RHPs with making teams, getting drafted and length of career. Consider these differences—
Regarding reputation, why is a LHP with minus velocity considered crafty while a RHP that throws with same speed thought of as a junkballer?
How come a LHP that throws 88-90 is considered a prospect while a RHP that throws 88-90 is considered a JARP (Just Another Right-Handed Pitcher)?
Baseball scouts repeatedly say a LHP has to give you a reason not to like him while a RHP has to give you a reason to like him.
If a LHP shows pitchability in the major leagues, he can find work for a long time i.e. Jesse Orosco, John Franco and Terry Mulholland.
A LHP that possesses the same traits as a RHP will always have more value simply because it is tough to find good left-handed pitching. It is very likely your team will lose a game this year to a LHP that might not make your team.
Hopefully this makes sense and I didn’t over-generalize or oversimplify too much.
(source: Inside Pitching)