By Tim Sullivan , UNION-TRIBUNE COLUMNIST Originally published July 30, 2010 at 9:06 p.m., updated July 31, 2010 at 12:02 Tra Thomas has become a fixture in pro football by making himself a moving target. Despite his massive dimensions — 6-foot-7, 318 pounds — the Chargers’ new lineman doesn’t stand still long enough to provide much shade. He’s always adding to his trench warfare repertoire, always building on a combative base. Boxing. Mixed martial arts. Bodyguard training. Show Thomas some useful twist, and he’ll strive to incorporate it at the expense of unsuspecting linebackers. Three times a Pro Bowl tackle with the Philadelphia Eagles, Thomas is an old dog open to new tricks. “As an offensive lineman, you’re in a fight the whole game,” he said Friday after the first full-squad practice of Chargers training camp. “I like doing stuff that makes my punches more efficient.” To demonstrate, Thomas reaches expertly for a reporter’s Adam’s apple, promising to be gentle, but inflaming the imagination and triggering the cringe reflex. For all of the precision and athleticism evident in the open field, football can be a brutal game at the line of scrimmage. If Tra Thomas is past his prime after 12 NFL seasons, he is not above taking whatever advantages avail themselves. He has joined the Chargers as holdout insurance, as an experienced hand who can help shore up Philip Rivers’ blind side in the absence of unsigned tackle Marcus McNeill. That McNeill remains unsigned is a tribute to bad advice and, perhaps, only a temporary condition. This is not to suggest that Tra Thomas has given the Chargers a lot more leverage with their incumbent left tackle, but Thomas has been there and done that through 168 NFL starts. He is unlikely to leave Rivers in traction. “Whoever lines up there I feel full confidence in,” Rivers said. “I won’t play one bit different. I think that shows the confidence I have in who that guy will be, and that’s no slight to Marcus. “I have no anxiety, haven’t lost a bit of sleep over it.” Granted, the day Rivers departs from the party line is the day the cows come home in Corvettes. The Chargers’ party line is that Marcus McNeill is not quite irreplaceable. “Tra is an outstanding pass protector,” Chargers coach Norv Turner said. “I think it showed up when he was here for three or four days in the spring. It jumped out right away. This guy’s got long arms and he uses his hands and he pass protects. Our defensive players, right away, they see it. … “Everyone talks about being out here in May and June in your underwear, but you can evaluate a guy’s ability to pass protect and you can evaluate a guy’s ability to pass rush. It’s almost like watching two guys play basketball. A guy who can play defense in basketball can play defense. A guy who can drive to the hoop and beat people, that’s a skill. It’s something you can practice and evaluate without pads on.” Efforts to evaluate Thomas based on his 2009 season with the Jacksonville Jaguars are inherently inconclusive. Signed to a three-year contract as a free agent, presumably as a replacement for Khalif Barnes, Thomas was subsequently relegated to an insurance role when the Jaguars spent their first-round draft choice on Virginia tackle Eugene Monroe. Thomas started three of the Jaguars’ first seven games last season, but became a spectator down the stretch. Though he once announced a goal of playing 20 NFL seasons, a lack of options caused Thomas to contemplate “shutting it down” before the Chargers called. “I had bought a boat,” he said. “Me and my family were cruising from Florida up to Philly. Then (the boat) broke down in Carolina. The next day I got the call to come out here. “I still have a love for this game. It’s not like I look at it as something that I dread. … And this was a good situation, coming to a team that’s already established. It’s easy to come to a team that’s successful.” It’s easy to make yourself useful, too, when you remain receptive to new ideas and continue to seek shortcuts to the other guy’s throat. “Before, I wasn’t much of a studier when it came to the guys I was playing against,” Thomas said. “When you have that athletic ability, you don’t really think about it too much. But now I find myself, even in practice, starting to study them a little bit to see what kind of stuff they’re doing. You don’t want to come out here and look sloppy. “Back when I first came in, you had your power rushers and you had your speed rushers. The power rusher was always on the right corner with the right tackle and the speed rusher was always over the left tackle. But then, I think, when Jevon Kearse came in, it changed, because you put a speed rusher over the right tackle and that kind of changed the game. Now you’ve got guys over the left tackle that are bull-rushing a lot more.” When Thomas was playing at 340 pounds, he felt puny when his weight slipped to 330. Now, at 318, he’s looking to lighten up. Once they’ve mastered their technique, veteran players tend to concentrate on camouflaging their declining quickness. Or adding new weapons to their arsenal. “Boxing was cool,” Thomas said. “It teaches you to keep your hands up, makes you comfortable with moving around and throwing your hands at the same time. As an offensive lineman, in pass protection, you’re doing a lot of that. You’re trying to be efficient when you’re throwing your hands. It makes you hit what you’re aiming at.” Bodyguard training is more specialized and, under current NFL rules, less applicable. Thomas learned how to disarm attackers armed with knives and guns, how to guard executives in a diamond formation and how to devise exit strategies in unfamiliar buildings. “They would have guys pop out on us with BB guns,” he said. “Then we get back to the hotel and this lady walks in and they kick in the door. There were guns shooting off. It was very realistic.” You wonder how that experience can be applied to pass blocking? Tra Thomas has an answer. “You are the Secret Service for the quarterback,” he said.