Need help with our drive system and electronics

Last year we ran into problems with our drive system.  We bought a Sabertooth dual 60A motor driver and used two RS775 Motors - 12V.  we tested the bot by driving it straight into the wall and going full speed forward then straight into reverse at full speed without any problems.  As soon we hit into another bot, it would completely shut down. Each motor has a stall current of 30 amps and the sabertooth has a max peak of 120 amps per channel so we can not figure out why it would shut down.  does any body have any advice on how to fix this?

Performance
Model M5-RS775-12
Operating v : 6v - 18v
Nominal v : 12v
No Load RPM : 7300
No Load A : 1.1A
Stall Torque : 61.1 oz-in 431.5 mN-m
Stall Current : 30A
Kt : 2.04 oz-in/A 14.4 mN-m/A
Kv : 608 rpm/V
Efficiency : 76.8%
RPM - Peak Eff : 7300
Torque - Peak Eff : 11.69 oz-in 82.6 mN-m
Current - Peak Eff : 5.7A

we are using a 16:1 gear ratio

a whyachi MS05 DC Power Switch

and we do not have a video of it. it only happens when it hits into another bot.  we have rammed it up against walls and nothing has happened and also basically sat on top of it and tried to make it move and it wont shut down like it does in the arena

What is a brown out?