Platoon. It's a unit in the military. It's a rotation of players at one position in sports. It's a way of life for the A's. Before Saturday, Oakland had a five-man platoon in the outfield (and at designated hitter), six players competing for two positions on the middle infield, and a two-man platoon at catcher. First base belonged to Brandon Moss, until the A's announced they had claimed Nate Freiman off waivers from Houston. Freiman, a four-year minor-leaguer drafted by the Padres in 2009, was taken by Houston in the Rule 5 draft, so if the A's do not keep him on their major-league roster all year, they must expose him to waivers and offer him back to San Diego. "We've been watching him for some time," said assistant general manager David Forst. "Our scout, Mike Ziegler, had been keeping an eye on him in Florida." Actually, the A's had been watching Freiman longer than that. They hoped, but didn't expect, to take Freiman themselves in the Rule 5 draft. "We didn't expect him to last all the way to us, and he certainly didn't," Forst said. Freiman hit .298 last year at Double-A San Antonio with 24 home runs and 105 RBIs in 137 games. At 6-8 and 250 pounds, he provides a big target at first, but his forte is offense.