A condition where the biceps of a person are malformed to resemble baseballs, caused by improper exercising techniques. Usually this happens when a person half-extends their arm when exercising over a period of time. For example, on a chin-up bar, the person never lowers their body below the half-way point (the farthest they extend makes their arms look "L" shaped). Once acquired, this condition is very difficult to correct. Not only does it limit the person's lifting potential, it looks unattractive to most people.
Hey check out that meat head over there, his baseball biceps look ugly as hell.
I'd better be careful of my lifting technique or I might be stricken with the infamous baseball biceps.
God damnit, I have baseball biceps. Welp, time for amputation.