American boxer Claressa Shields has successfully defended her London 2012 gold in the women's middleweight division, beating the Netherlands' Nouchka Fontijn in a unanimous decision Sunday.

Standing 5'8" to Fontijn's 5'9", Shields showed her versatility and speed in this fight to win her second gold medal.

Shields, 21, set the tone early, coming out swinging with a wicked hook aimed at Fontijn, 29. But Fontijn showed herself to be elusive, bobbing out of the way of some of Shields' most dangerous blows. She also kept a left jab ready, to try to fend off Shields.

Looking for an opening, Shields stalked Fontijn around the ring, bursting toward her with a quick jab. In one exchange, Fontijn landed both a left jab and a solid right to Shields' head.

We'll remind you that the women in Olympic boxing are still wearing headgear – equipment that the men have now done away with.

The second round saw the boxers switch roles at times. While Shields had been stalking Fontijn around the ring in the first round, in the second she changed her footwork – and in one artful sequence, she backpedaled smoothly out of trouble before landing a solid right on Fontijn.

The crowd, loud and rowdy, enjoyed this fight, particularly when both boxers showed a willingness to stand nearly toe-to-toe and trade punches.

In the third round and again later, Shields showed her unconcern with being hit by Fontijn, dropping her gloves to her waist so she could wind up big punches. Some of those landed – and Shields followed them with a flurry of other hits.

By the fourth round, it was Shields' fight to lose, and she again dropped her fists and used her quickness to dodge Fontijn, bobbing left and right. As before, she then went back to work, putting her gloves up and punishing Fontijn with hard, looping punches anytime she got too close.

In one sequence, Shields countered a Fontijn punch with a hard right hand to her opponent's chest, before landing a powerful left.

After the match, Shields was ecstatic. With her victory declared, she did a cartwheel in the ring. When she stepped out of the ring, she took a U.S. flag on a quick victory lap around the arena.