It was a lazy, hot summer day in Santa Clara, Calif., with San Francisco 49ers fans in attendance realizing that a training camp practice is not all that exciting. The staffer in charge of tunes put on a 30-year-old classic, and almost on cue, running back Christian McCaffrey started high-stepping.Return of the Mack (Oh my God) / You know that I’ll be back (Here I am) / Return of the Mack (Once again)At this point, McCaffrey was well on his way back from calf, Achilles and knee injuries that derailed his 2024 season, and the song was fitting. But he was not, by any means, dancing to celebrate his return. He was locked in.McCaffrey is always locked in. He probably does high knee bends on his way to the meeting rooms, kitchen and to re-swaddle his baby girl at night.“He is a psycho in a good way,” 49ers coach Kyle Shanahan said.McCaffrey never stops, and his return has helped spark a 2-0 start for the 49ers heading into the home opener against the Arizona Cardinals on Sunday. He is tied for the NFL lead in receiving yards by running backs with 125 and also has a receiving touchdown and 124 yards rushing. After all the last-minute intrigue of a calf tweak and whether he would play in the season opener, McCaffrey led the NFL in Week 1 with 31 touches.People with special, uncharted amounts of drive don’t waste much time describing it. But we gave it a shot anyway.“I don’t know, man. I just approach life that way, and I love football,” McCaffrey said, smiling, before practice Wednesday. “It comes out of love. I work really hard because I love what I do.“I feel like I’m the luckiest guy on the planet. I get to play football in the NFL with some of my best friends.”The 49ers have a core of star players, and McCaffrey has pulled aside some of those friends, including quarterback Brock Purdy, to remind them of this precious window they have right now.“You’ve got a limited time to do this, so you might as well give your all,” he said. “You can relax and all that stuff when you’re done. … I really do love it. It’s a special sport, and it’s really fun when it’s played the right way, but it takes a lot of work.”McCaffrey, a year removed from being the Offensive Player of the Year, missed 13 games last season and, at one point early this spring, told Shanahan, “I’m back.”That’s according to Shanahan; McCaffrey has no recollection of it.“I probably told him that,” McCaffrey said. “I always look at it like that. Any time you’re stepping on a football field, you need to have full confidence in yourself coming in.”His teammates couldn’t have more confidence than when he is on the field with them.The 49ers are 25-8 with McCaffrey in the lineup and 5-9 in the games he has missed since trading for him in 2022. Better yet, San Francisco is 16-1 in games in which McCaffrey has 16 or more carries and 9-7 when he doesn’t. Last Sunday, in New Orleans, the 49ers analytics team said McCaffrey turned in his most efficient game — yards gained over expectation — as a 49er, according to general manager John Lynch.“Getting in and out of cuts, running hard, he’s back to the McCaffrey that we all know,” Purdy said. “And then mentally, he’s on one, like he’s ready to play a whole season and go hard.”McCaffrey was telling teammates all spring and summer that he couldn’t wait for the season to start. And then, early on in training camp, left tackle Trent Williams was one of the first to sound warning alarms around the league: McCaffrey was indeed back.