Definitions of ringer:

• noun:   (horseshoes) the successful throw of a horseshoe or quoit so as to encircle a stake or peg
• noun:   a contestant entered in a competition under false pretenses
• noun:   a person who is almost identical to another
• noun:   a person who rings church bells (as for summoning the congregation)
• name:  A surname (rare: 1 in 50000 families; popularity rank in the U.S.: #6523)