McWilliams Arroyo received the flag of Puerto Rico for the 2008 Olympic where he joined along with his brother.
On July 2, 2008, Arroyo was selected to carry Puerto Rico's flag in the opening ceremonies of the Olympics. The Arroyo twins, McWilliams and McJoe, qualified to the 2008 Summer Olympics due to their performance at the AIBA World Championships. It was the second time that twins competed in an Olympic boxing tournament, the first pair being Valeriy and Wladimir Sidorenko, who participated together in the 2000 Summer Olympics. 
