Question

To my teacher and master, the great Rabbi Michi, may he live long and well, greetings.
 
Hullin 91a.
 
“Like a person who embraces his fellow and his hand reaches the socket of his fellow’s right thigh,” etc.
And see Rashi, who explains: one who embraces his fellow from the front, and “his right hand” reaches the socket of his fellow’s right thigh from behind.
And so too Rashi writes on 90b, s.v. “his reasoning inclines” — for ordinarily, when one wrestles with his fellow, he puts “his right hand” to the other’s left side, embraces him, and his hand reaches behind him as far as his right thigh.
 
However, see Rabbenu Gershom on 91a: “Like a person who embraces his fellow” — that is, his “left” hand reaches the socket of the right thigh.
 
It requires clarification: what exactly are they disagreeing about? At first glance, the straightforward reading seems to fit Rashi.
 
Signed with great respect,