Physically Awkward

 On an early page of Claire Messud's novel The Emperor's Children, I read

A big, physically awkward man with a square head and jowls, Frank Clarke had been a Green Beret in Vietnam, which was where he had met Thu, Julius's mother, after whom the boy took.

I suppose that "physically awkward" is to contrast with the asserted grace of the son. But do the physically awkward make it through the training required to qualify for the Special Forces, or any elite infantry force? One of my high school teachers, who was also the wrestling coach, had served in the Special Forces.  He was not at all physically awkward. Frank Clarke seems me more prop than minor character.