During his run (as Stanley Kowalski) in the Broadway production of "A Streetcar Named Desire," Marlon Brando rigged up a punching bag in the theater's boiler room and invited Jack Palance to work out with him. One night, Palance threw a hard punch which missed the bag and landed smack on Brando's nose. Brando had to be hospitalized and replaced by his understudy. His understudy? Jack Palance, of course.
(Palance's reviews helped land him a contract with 20th Century-Fox.)
[On another occasion, while filming a fight scene with Burt Lancaster, Palance (an advocate of method acting), punched his unexpecting co-star in the face. Lancaster responded by socking Palance in the stomach, causing him to vomit.]