Beginners can be spastic, unpredictable, jerky, and usually also doesn’t know the rules of the game yet.
All that thrashing around, lack of control, as well as potential ego issues means that there’s a pretty high likelihood of something going wrong. Either that dude planting an elbow in your eye, or not him tapping out when he’s in a Kimura, or doing something else stupid.
Here are my thoughts on how to safely train witih a newbie in a way that nobody gets hurt and everybody gets better. Hope it helps you or someone you know!