Brushless ESC Question (braking)

Ok,
So, I got back from the track earlier today after a not so successful day.
Long story short, I let a nitro guy try out my buggy and he did his best to beat the crap out of it, first he stripped the plastic spur gear (a few minutes after he said "hey something sounds weird you should check the gear mess", but he kept driving).
After I swapped out the spur he decided he wanted to play with it some more and he got about two laps around before cracking the ball-cup on the front universal shaft.

So... Finally to my question:
I am running a HV4.5 with the HV maxx ESC and a Spektrum DX3.0
I just got back into RC last year (was involved maybe 10ish years ago before motor braking). How does one activate the motor brake while having reverse enabled?
The nitro guy was pushing the throttle to the reserve position when he wanted to use the brake. In the past I just let off the throttle and the buggy would slow down adequately enough for me. Are you supposed to throw the throttle trigger to reverse to brake? if so, how does the ESC know you want break not reverse?
Essentially, aside from wanting to know how to properly use reverse, I want to know if him using reverse as brake (if that is what he was doing) was the cause of breaking the universal shaft, or if it was just a weak part.

Any thoughts?
Thanks