“the hollow of his thigh.” That is, the socket of his hip. In this battle, though the “man” could not seem to prevail against Jacob, at the same time he showed Jacob he could win the contest whenever he wanted.
“was strained.” Although many versions say “dislocated,” that is not likely because then Jacob would not have been able to walk at all. The reading “strained” (JPS; TNK) or “wrenched” (NIV) is much more likely. It is extremely difficult to put a dislocated hip back in place, and it seems unlikely that Jacob could have done it.