I think it is in the down, and therefore safe, position, that is why he is doing it.
As far as covering it with plexi, won't that add the weight back? Why not paint it bright yellow and inform all mentors, visitors, and engineers that it is a highly dangerous device that is likely to go postal at any second. That should keep them away.
For past "guillotine" bots, our rookie bot last year had a strange knack of having parts of the elevator drop at extremely dangerous rates.
Pictured here
Only one person got hurt but he is adapting to his hook just fine

A few people did get a few finger pinches but nothing serious.
Chris McKenzie
2186
__________________
Working on Robotic Eagles group(PM for info)
Stephen Colbert-"Please tell me this leads to robot
battles."
Dean Kamen-"It does lead to kids building robots, and they do compete in the sport but we also teach the kids gracious proffesionalism, so while the robots are competing, they do it in a very, very gracious way."
Darn, I got into this for the battles!