>>106490389
This is how I put sfx in my games
*pew pew*
https://www.youtube.com/watch?v=d4cLCopfa-s

Can/do companies really go after indie devs or there's a popularity/money made off of it threshold below which you're safe?
that entire depends on how the company in question wishes to proceed so there is no one answer to that.
Honestly, just record punching an A4 paper as if you want to make a hole in it like in never back down 2 movie. Then fire up a DAW like Reaper, trim, high pass filter and boost. That will be good enough.
You can also just get some sound from a royalty-free game sound effects, google search will pop up a few.