In baseball, what type of pitch puts most stress on a throwing arm?

Anything that curves, like Slider,curve or a slurve.

Remembering Sandy Koufax, I would have to say the curve ball.

The act of throwing a baseball is hard on the arm, no matter what kind of pitch you are making. In general, any kind of 'breaking' pitch (i.e. not a fastball or change-up) are the pitches that hurt arms more.

Back in the late-1980s/early-1990s, a rash of arm injuries was blamed on the popularity of the 'split-finger pitch' or 'forkball', but that may have been coincidental.

http://en.wikipedia.org/wiki/Split-finger_fastball

http://en.wikipedia.org/wiki/Baseball_pitching#Pitching_biomechanics

i have heard that the change up is bad.

Submarine pitch, Toughest pitch to do successfully, I was able to do it in high school, but could only last a few innings. The batter had no clue what was coming.

http://www.youtube.com/watch?v=HobjeN8guZY

It's just barely outside of being underhand, so it's just barely a legal pitch in MLB.

I've heard that the slider puts the most stress on your shoulder & elbow. I remember seeing a 60 Minutes piece about kids in Little League getting injured by throwing sliders & an effort to get the pitch banned.

I've been a pitcher my whole life, and the answer is definitely a curve ball. With that said though, it has a lot more to do with your mechanics. I try to tell young pitchers, and I wish someone would have told me earlier to fall towards the plate when you throw, with your front leg stiff. Make sure your legs are very strong. Your arm has to just be the catapult, if you will. Let the strength and energy come from your legs and hips.

I've not been a pitcher but I have played in high school and one or our young players had a really good curve but ruined his arm and ended up playing shortstop.
I would think that a pitch breaking to the right for a right hand pitcher or to the left for a left hander. The left breaking curve for a righty and a left breaking one for a lefty would really stress the elbow.

Well, the curve ball and screwball comes to my mind. Pitched in high school and college and these two pitches put more stress on my arm. +5

The answer is the "curveball". The most common way to injure the ulnar collateral ligament [Tommy John], is with repetitive or forceful overhead throwing of this pitch. The force on, and the rotation of the forearm needed to throw the curveball.. can cause the ligament to stretch and tear. Surgury required. In younger athletes, for whom the growth plate (the medial epicondylar epiphysis) is still open, the force on the inside of the elbow during throwing is more likely to cause the elbow to fail at this point than at the Ulnar Collateral Ligament. This injury is often termed "Little League Elbow" and can be serious but does not require reconstructing the Ulnar Collateral Ligament. Follow the sage advice and direction of 'Sensaye' [posted above; July 27th, 2009]... "Make sure your legs are very strong.... Let the strength and energy come from your legs and hips."

a screwball...it pronates the hand which is hard on the arm!!