When they are doing their jobs, they are not looking at what is happening on the field. It would make sense to have someone standing just off camera who is watching what is going on and can protect them.
or a simple $10 net
well, if on the field during batting practice or other practice, they need to have someone paying attention.
If I recall correctly, a minor league 1st base coach was killed by a foul ball. That’s why base coaches wear batting helmets nowadays.
And, teams have been extending netting along the baselines, to protect fans from line drive foul balls. There have been fan injuries due to foul balls.