i have never had a student have this kind of accident doing this kind of practice. but then also, i get the kind of students who dont get upset about getting hit, even if its an accident. one thing i learned from a good friend about students, you get who you go after. any new person who comes in my doors knows what type of school i have, and i make sure they know what to expect. when i think a guy doesnt have it in him, we have private lessons, so i can help him build up or decide if our school is the one for him. if you go after soft students or fit your school around these kind of people, then thats what you will get.
i am not saying that all of my students have pain tolerance coming through the door. but pain tolerance is something you can teach, and good fighting instructors teach it.
as for as control, if he does not have enough control to be able to do a simple 1-6 and not hit his partner, he is not coordinated enough to learn fighting martial arts. but an adult with a full brain should be able to do this. but accidents happen, and i make sure all of my students know to expect it.
PS
one thing about accidents and injuries. it is something the fighting arts students needs. if you think you are a fighter but you panic when you get hurt, you will only be able to win fights against weaklings and people in wheelchairs (actually i met one who can fight pretty good). if you are a teacher of the fighting arts, you cannot try to protect your students from injury like they are children. like it or not, pain and injury is part of the learning process to arnis and eskrima, have you ever met an eskrimador who never had a broken finger or injured hands or arms? when these things happen, they make the fighter stronger and more resistance to panic when he experiences it.
2 examples: i had a student who got his nose broken in sparring. by the way, he had 2 black belts already, and he owns a school in my city. anyway, after one of my students who was a doctor straightened it, i made him get back up and finish his match, and he did pretty good. this was a lesson to everyone about fighting an opponent with a painful injury. he learned something that even i didnt learn, which was, what does it feel like when i fight with a broken nose.
two months later i was sparring with a student who had a instructor ranking in serrada, and he broke my thumb. in front of my whole class, i had to finish my match, and still spar about 5 more students in class (there was 15 in my class, and everyone got one round with me). anyway, i was in pain ( i didnt know it was broken then) and it was HARD. but hey at 31 years old, i finally learned what my own student learned before me. (we were stickfighting that day)
any student who is being told he is learning COMBAT, who is being protected from pain at the same time, is being cheated.