What does the saying a pawn in the game?

In the game of Chess, a pawn is a 'man' (piece) of the lowest value, therefore

if you say someone is just a pawn means his place is not important in the scheme of things. It also implies that he has been manipulated.

When Oswald was arrested after President Kennedy was shot in Dallas, he claimed he was just a "patsy" or fall guy; he could have said, "I'm just a pawn."