Numbers 1 and 3 on a rugby team. # 1 is the loosehead prop and #3 is the tighthead prop. Their job is to support the hooker.
A loosehead prop lines up for the scrum on the left hand side of the hooker in the front-row, and the tigthead on the
right hand side of the hooker. When the two front-rows
interlock with each other for the scrum, the loosehead has one side of his head out of the scrum (the left side), and scrummages against the
opposition tighthead. The tighthead has both sides of his head in the scrum, and scrummages against the loosehead.