[kcroyalgm]

Low is probably half the real life rate.
There are lots more injuries in real life than most people imagine.
That said, OOTP Classic setting results in a lot of injuries, probably closely resembling real life.
But realism isn't everything.
Lots of injuries, especially long, SEI, and CEI injuires, have a severe negative impact on GM retention.
It's not a lot of fun to play a game where lots of your key players get hurt a lot.
Fun does matter.
The low setting provides for annoying injuries while not making the injury rate a critical factor in team success.
There's plenty that's not realistic in OOTP - like who gets designated a class A free agent and who doesn't, just as an example. Or like you can't have non-roster invitees to spring training as another.
SO:
If realism is your goal, go with OOTP Classic or higher.
If enjoyment and GM retention seems more important to you, go with low for the injury setting.