I just watched the Machado slide and it's basically nothing. Pedroia's positioning is fine, Machado's leg pops up and he spikes Pedroia. Doesn't even really make strong contact with Pedroia's leg. I'm seeing online descriptions saying that Pedroia's knee "buckled" and so on - nope. He got spiked, his leg popped up, and then he went down. If it truly ended his career, it's an amazingly innocuous play for that to happen on:
https://www.youtube.com/watch?v=rbAYcXPhIUE