Gabe Kapler once had a season ending injury running hard and tripping over 2d on a close-to-the-fence home run. The guy who hit it had to wait behind him while the trainer came out, took Kapler off the field, and Kapler's replacement was allowed to finish running the rest of the way. An incredibly obscure rule that either Kapler or the hitter knew.
Heck the umpires said that they had never seen the rule enforced.
Tony Graffanino hit the homer, Alejandro Machado pinch ran and Gabe Kapler ruptured his Achilles' tendon.
(1) If an accident to a runner is such as to prevent him from proceeding to a base to which he is entitled, as on a home run hit out of the playing field . . . a substitute runner shall be permitted to complete the play."