Sledgehammer is a 1983 horror film written and directed by David A. Prior.
In a remote house, an abusive mother locks her young son in a closet, then goes into another room to meet the man she is cheating on her husband with. The man and woman intend to abandon their respective spouses, but their plans are cut short when the boy escapes the closet, and murders them with a sledgehammer. The bodies of the adulterers are found by the authorities, but the boy is not, and he is presumed dead.