DENVER -- Bryce Harper is getting daily treatment on his back, which he tweaked while diving for a ball June 7 against the Mets. "I've seen him with all kinds of contraptions [on his back], but I think right now it's for prevention," Nationals manager Davey Johnson said. Harper has started all but one game since being called up on April 28. He's drawn attention for, among other things, his aggressive style on the basepaths and in the outfield, playing at times like his hair is on fire. "The one thing I never try to do is turn down somebody's aggressiveness, it's hard enough to try to turn it up," Johnson said. "I like to see everybody play all-out. With experience, [Harper] will feel that warning track and realizes he doesn't have to be going 100 miles per hour." In his previous 10 games before starting Monday against the Rockies, Harper had a .205 batting average (8-for-39) with 11 strikeouts, one RBI and no homers.