Physical Danger
There's not a lot of physical danger involved in subbing. Occasionally, you'll hear some horror story about a sub who found themselves on the wrong end of a physical confrontation. But that's a rarity. For the most part, you'll just be served a heaping helping of emotional and verbal abuse. Not physical.
Kids may yell at you and call you names. They'll play pranks on you, and stick things on your seat. But you're not going to be hurt—probably. If anything like that ever happens, the response from the school administration is going to be immediate, and they'll be more than happy to dole out punishment for you.
You don't have to be a cage fighter or specialist in the armed forces to substitute teach. You just need a lot of patience.