Is it Safe to Throw a Breaking Ball? An Editorial

Every spring, the weather warms, the grass again turns green, and the prospects of a new baseball season are born. We as sports medicine physicians can also look forward to receiving the same question we are asked by parents every year: is it safe for their young athlete to throw a curveball and at what age? This is not such an easy question to answer and continues to be a point of debate. I believe a lot of the confusion stems from the limitations of the existing literature we have on the subject and a deeper dive and considerations are needed before arriving at a conclusion to the question.

In 2002, Lyman et al ⁴ reported that “breaking pitches” were a more dangerous pitch type, with the curveball associated with a 52% increased risk of shoulder pain and the slider associated with an 86% increased risk of elbow pain. The authors recommended players 9 to 14 years of age not throw breaking pitches. Fleisig et al ³ demonstrated in collegiate-level pitchers that joint load was not significantly different between fastballs, curveballs, and sliders; however, the question of risk remained for the youth pitcher throwing breaking balls. Dun et al ² reported that elbow and shoulder forces and torques were significantly less for the curveball compared with the fastball, which would imply that the curveball may not be more harmful than throwing a fastball among youth-level pitchers. While this was viewed as support for curveballs in younger throwers, the fact that these findings were different than collegiate-level pitchers lends to the notion of whether younger players are throwing these pitches correctly? There are important considerations here that I believe are worth exploring in search of the answer.

A curveball is a type of “breaking ball,” as is a slider. The difference between the curveball and the slider are the characteristics of the pitch trajectory and the grip and wrist action performed to accomplish it. The curveball has an action during which the ball travels in a path from 12-o’clock to 6-o’clock on a clock face. More commonly this is from 1-o’clock to 7-o’clock for a right-handed pitcher and 11-o’clock to 5-o’clock for a left hander. The velocity is generally more than 15 mph slower than the fastball.

In contrast, the slider is intended to look like a fastball and then “slide” away from the hitter with an oblique tilt to its trajectory. On the clock face from a right-handed pitcher, this would be 2- to 8-o’clock, for example, but the break is shorter and later as the pitch reaches the plate. Although the slider can be up to 10 mph slower than the fastball, it has more velocity than a curveball.

To throw a slider or curveball, the index and long fingers will be next to each other off-centered on the ball, and along or over a seam. However, a major difference exists between throwing “breaking balls” and other types of pitches. The curveball demonstrates the greatest forearm supination and the curveball and slider both have greater ulnar deviation compared with fastball and change-up pitches. ⁷ This distinction is, in my opinion, of great importance when discussing throwing a breaking ball versus a fastball. The flexor carpi ulnaris (FCU) and the flexor digitorum superficialis (FDS) are the most active forearm muscles that stabilize the elbow dynamically against the valgus torque associated with throwing. The FCU is both the most important and intimate anatomically with the ulnar collateral ligament. ⁵ With the known ulnar deviation of throwing a curveball, the FCU is actively firing and the FDS is presumably more active during both the curveball and slider as the proximal interphalangeals of the long and index fingers are more flexed with the ball gripped tighter than a fastball. Remember Crash Davis telling Nuke LaLoosh in Bull Durham: “hold it like an egg?” Yes, you hold a fastball like an egg, whereas with breaking balls you do not. Thus, could it be reasoned these pitches cause more fatigue of the flexor-pronator mass than when throwing the fastball? This potential decrease in dynamic stabilization could, in turn, expose the ulnar collateral ligament complex to higher forces.

It is important to remember that, despite the best intentions of coaches at the younger age levels, they may not be knowledgeable enough to teach appropriate techniques of throwing breaking balls. Furthermore, does a younger player even have the hand size to be able to do anything more than just hold it in a fashion so it does not fly out of the hand when throwing? In my observations, the amount of rotatory motion at the elbow in a younger pitcher trying to throw a breaking ball is more pronounced than is seen in a more musculoskeletally mature athlete. This could be due to either not having the hand size to perform the appropriate grip or they technically do not know how to throw the pitch correctly. In an attempt to make the ball “curve,” they rotate the wrist and the elbow at the point of ball release. I bet if you think back about when you were young and tried to throw a curveball you probably did the same thing. If the physis is still open, these rotational loads could place the younger player at increased risk of stress-related injuries. ¹

In the end, the incidence of young throwing arm injuries remains concerning and debate continues ever since Lyman et al ⁴ first recommended that pitchers between 9 and 14 years of age do not throw a curveball or slider. The risk of medial elbow pain continues to be higher in youths than in older players. ⁶ Thus, although it is an attractive prospect to make a hitter swing and miss or fool him with a curve ball, mastering command of the fastball and change-up will serve a young pitcher much more in the long run. Make no mistake, breaking pitches are an important part of pitching and pitching with success. We just need more clarity of when youth athletes can start throwing them and ensuring they are throwing them correctly. So, getting back to the question of “is it safe to throw a curveball?” At this point, I still utilize the insightful wisdom of Dr Andrews, who recommended not throwing breaking pitches until old enough to shave. Is there rock-solid science behind this recommendation? No. Does the dogma make sense? Absolutely! Unfortunately, at this time the waters are still murky and we need to continue to perform strong methodological studies to ultimately arrive at the most appropriate recommendations.

—Michael T. Freehill, MD
Associate Professor of Orthopaedic Surgery
Stanford University School of Medicine
Executive Director, Stanford Baseball Science Core