10 matches would be correct
5 man RR: Wrestlers A,B,C,D and E:
A against B,C,D,E = 4 matches
B against A,C,D,E = 4 matches
C against A,B,D,E = 4 matches
D against A,B,C,E = 4 matches
E against A,B,C,D = 4 matches
Five wrestlers, four matches each (5x4 = 20) equals twenty matches.