a wrestling hold in which one arm of the opponent is twisted upward behind the opponent's back
See hammerlock in American Heritage Dictionary 4
(hămˈər-lŏkˌ)
noun
A wrestling hold in which the opponent's arm is pulled behind the back and twisted upward.
Overwhelming dominance that is difficult if not impossible to overcome: “has preserved its hammerlock on the business largely because of its reputation for quality”(Fortune).