Volstad, slotted No. 4 in the Marlins' rotation, has struggled this spring with his sinker. But he has made progress in the last two starts"Going into the season, I couldn't ask for anything more than that," he said. "The hitting was just secondary but the pitching part was good. I'm just trying to continue what I've been doing in my last couple of starts."The Marlins rotation is set with Josh Johnson, Ricky Nolasco, Anibal Sanchez, Volstad and left-hander Nate Robertson, acquired Tuesday in a trade with Detroit.After the game, Florida sent right-handers Rick VandenHurk and Tim Wood to Triple-A New Orleans, leaving right-hander Clay Hensley with the final bullpen spot.Right fielder Cody Ross has been out since March 23 with a sore right calf, and his progress has been slower than expected."I'm not going to lie to you: It's concerning. It really is," manager Fredi Gonzalez said. "You go into the major league season, you may not have that guy."If Ross opens the year on the disabled list, outfielder Bryan Petersen could win a roster spot. Petersen, who played in Double-A last year, is hitting .295 in 23 games.Nationals right-hander Garrett Mock, trying to win a rotation spot, allowed six runs (four earned) on seven hits in 4 2/3 innings."The outing speaks for itself. I can't say much about it. You saw it," manager Jim Riggleman said. "He was good for two or three hitters in a sequence, and then he would throw to a couple of hitters and leave some balls up in the zone to be hit."