Aggressive fighting move. The assailant raises one arm above his own head, places the other along his leg, and then brings them together in a rapid motion on another's body in order to cause injury; the arms make a motion similar to that of a clam. Example: I was really kicking john's behind until he clam slammed me right in the face.
CLAM SLAM
Meaning of CLAM SLAM in English
Slang English vocab. Английский сленговый словарь. 2012