Competition on the football field officially starts Friday for the San Francisco 49ers. Players will report on Thursday, where they’ll perform a conditioning test and check in with position coaches.

A year after Chip Kelly’s rather delicate training camp based more on mastering the timing of his up-tempo offense, the tone will be a tad different. A tad louder, with crunching sounds.

“I want it to be physical,” Kyle Shanahan said about training camp on June 14. “It’s just a standard, how you practice.”

A combination of factors will make Santa Clara one of the more hard-hitting and competitive training camp locations around the league.

Shanahan and John Lynch are going to demand excellence and there are two types of players that now exist on the roster: Trent Baalke-drafted holdovers (27 of them, to be exact) and a wave of rookie players brought in (28, to be exact). In several instances, the two separate factions will be going head-to-head for jobs. It’s going to create an organic football bubble of competition oozing with more pure football players and less of Baalke’s big strapping athletes.

So the competitive feel will reach a fever pitch, a much-needed aspect that’s been missing from the 49ers. But there are ways Shanahan uses the increased clashing into an X’s and O’s advantage.

It’s specifically the run game where Shanahan values this time for physicality from the offensive linemen. They have to start learning how to work together in his often tag-teaming zone-blocking scheme. Former Shanahan players, especially in Cleveland, will attest this practice time in August led to success later in the season.

“When we get these shoulder pads on, it’s more the run game, the protections, everything is physical as can be without taking your feet off the ground, and going after guys and taking people to the ground tackling,” Shanahan said. “You’ve got to do it then, because you don’t have that option throughout the season.”

Here’s the thing. Several key 49ers are coming off significant surgeries or season-ending injuries. And when you have competitive football practices with bodies flying around, scary things can happen.

–NaVorro Bowman: Tore his Achilles against the Cowboys on Oct. 3.

–Reuben Foster: Underwent shoulder surgery on a torn rotator cuff in February, a surgery that Adam Schefter reported scared teams off.

–Brian Hoyer: Broke his arm on a freak play Oct. 21 against the Packers.

–Arik Armstead: Underwent shoulder surgery in November after playing through pain much of the season.

–Carlos Hyde: Season ended on a gruesome hit that injured his shoulder.

Shanahan understands this. He’s conscious of it all and will hold daily meetings with head trainer Jeff Ferguson. Losing a key player in August can derail an entire season. There won’t be very much tackling.

“You’re at the NFL, you better know how to tackle or you’re not going to be there long,” he said.

And every single day won’t be physical. Shanahan wants to teach his players how to practice fast and safe — because that’s how most of the regular season will go. Perfecting the craft of going through a strong practice without hitting and still feeling accomplished is a sign of a good football team.

It’s a tricky first balancing act as a head coach. He wants his players fighting their asses off for starting jobs. He wants to establish a tone where there are clear winners and losers walking off the practice field. He also wants everyone fresh and ready for the regular season.

Again, the physical nature of the practice is way more for the linemen than it is for roughing up skill players. Shanahan has a cast of characters to sort through at offensive line. He’s added Jeremy Zuttah, Tim Barnes, Brandon Fusco and Garry Gilliam to an already pretty crowded unit. The coach needs them cranked up as much as possible to simulate the zone-blocking style — but without one of these 300-pounders hurting a prized young defensive linemen like Solomon Thomas or DeForest Buckner.

And of course, there’s more. A first-year regime building a foundation wants to mentally challenge players (even established ones) in practice settings. The theory goes, the mental stress during the week will help on Sundays. Shanahan and Lynch want to see how veterans like Bowman and Hyde react to the pressure of younger players infringing on their playing time. Catering to veteran players and giving them preferential treatment is not the type of culture Shanahan and Lynch are bringing.

They want to see if George Kittle and Trent Taylor are sharp enough to leapfrog established players on the depth chart. None of that truly reaches its height if he tones down the physicality. Players notice. They’ll be on high alert.

Training camp will have a different feel this weekend in Santa Clara. Now you know a little bit why.