You want to be careful when training Jiu Jitsu. You have to make sure you can train again tomorrow.
First of all before sparring you want to make sure you warm up properly so your muscles are limber.
You never know who you may end up sparring with.
When you have trained for many years at many different places you should realize not everyone rolls at the same pace or has the same body awareness. Heck, not everyone knows the gym rules.
If a person is what you consider dangerous then you should tell the person if you have an injury in case you are worried it could get worse.
It’s also important to be in positions that you consider safe for you. It may even be on bottom side position. You should likely try to keep your limbs close to your body if you are in fear. Be ready to tap at all times.
If the person is “herky jerky” try to stay in close contact to avoid getting elbowed in the b*lls or take a knee to the nose.
You get the drift. You never know where a person is coming from mentally or their body awareness so be sure to keep your ego in serious check if rolling against a reckless type of person who has no regard for your safety.
If you can avoid them to save your body do so. You don’t want to be the 50 year old recreational guy trying to hang with a 20 year old super athlete who could surprise you at any moment. A beginner can be especially surprising also. If a person ever gets angry go extra light even if you are pissed. I’ve seen injuries occur when two people lose their cool.
I’m not saying you MUST avoid anyone. Just be smart out there. Too many people “trained” Jiu Jitsu who no longer do and they have stories of injuries to tell.
How do you like to spar when you have to spar with someone you consider “dangerous?”