I have another theory as to why baseball managers wear uniforms. Dave’s doesn’t make sense because at times, basketball coaches get involved in brawls. Remember Jeff Van Gundy hanging on to Alonzo Mourning’s leg?
In baseball, you have coaches who are out on the field. that is, first and third base coaches. It would look a little silly for them to be out there and not wearing any kind of uniform at all. So they do. That makes sense. Well since all the assistants are wearing uniforms, the only sport in which they do, again, it would look strange if the manager didn’t also. That’s my theory.