Budoshin Ju-Jitsu
The Gentle Art of Self-Defense

Don't Break Your Thumb In Randori Or Grappling

#1 When you grab a gi in randori/grappling it is common to see competitors grab their opponent’s gi with a grip where their thumb grabs the gi from underneath [or opposite their fingers & palm] like when you normally grab something.
#2 While this is a more secure grab it can also entrap the thumb if the uke rolls as is shown in this picture and the next one.
#3 A broken thumb [or wrist] is a common injury if the uke rolls out of the throw or rotates during groundwork as your thumb &/or hand can become trapped in the twisted gi.
#4 An alternative grip is to keep your thumb next to your fingers & grip only with your fingers. This way you can easily slip your hand out of a twisted gi & prevent injuring yourself.
#5 The same problem can occur if you grab your uke’s obi with your thumb underneath. 
#6 The preventative solution is the same & your technique won’t suffer.