SCOTTSDALE — Team USA is absolutely loaded, but the roster only has four outfielders, and there’s no need for veteran infielders like Bryce Harper and Alex Bregman to play nine innings on March 3. That left manager Mark DeRosa with a dilemma in the late innings of Tuesday’s exhibition at Scottsdale Stadium.The Giants had sent DeRosa 11 of their prospects to fill the gaps, and as he started to remove some of his best players, he walked through the dugout and tried to piece together his infield. When DeRosa asked who could play third, Gavin Kilen raised his hand. There was no need to mention that he had not played the position since his freshman year of college.“I was like, man, it’s a once-in-a-lifetime opportunity,” Kilen said later. “I can do whatever you need me to do. I’ll play third if you need me to.”DeRosa simply needed the prospects to pinch-run and be available to warm up quickly if a big leaguer approached his pitch count. But because the game was such a blowout — Team USA won 15-1 — the young Giants ended up combining for 11 at-bats. Kilen, last year’s first-round pick, and Dakota Jordan...