Newton’s third law states that for every action, there is an equal and opposite reaction. That’s the case so far for 49ers cornerbacks and wide receivers as they compete entering the second week of Chip Kelly’s training camp Tuesday.

In clashes of one-on-one, seven-on-seven and 11-on-11 drills, the 49ers pass-catchers and defenders are battling. Both positions feature some of the most hotly contested depth charts on the roster. There are several prominent roles up for grabs.

When the season begins, San Francisco’s receivers should expect a heavy dose of press coverage, which has been exactly what they’ve gotten through the first week of camp. The defense had the clear edge through the first seven practices.

“It’s kind of a growing theme,” Blaine Gabbert said, “but it’s great work for the wideouts. Seeing press man day in and day out, it just helps them fine tune their craft, helps us get our timing down for man coverage because it is a lot different than free access versus zone. It’s going to do nothing but help us in the long run.”

Kelly agreed, pointing out the aggressive style his secondary employed during the early portion of training camp has been tough on receivers. The physicality could change this week with the addition of NFL referees to practice, which might limit contact downfield.

“There have not been many uncontested throws in any of our drills that we’ve done against the defense,” Kelly said. “I think they’re around the ball. I think they’re knocking the ball out. We’ve had a couple picks.“

Outside of the veterans Torrey Smith and Jerome Simpson, young receivers have struggled to get open. It’s easy to see why. Only two of San Francisco’s 12 receivers, Smith and Simpson, were selected before the fourth round of the NFL draft.

Six of the team’s wideouts were undrafted free agents, including Eric Rogers, who is done for the season after tearing an ACL. DeAndrew White, Dres Anderson, Bryce Treggs, Devon Cajuste and DiAndre Campbell form that group.

The 49ers used fourth-round picks on Quinton Patton, Bruce Ellington and DeAndre Smelter before selecting Aaron Burbridge in the sixth round this spring.

In contrast, seven of the 49ers nine cornerbacks were drafted, and one of the undrafted free agents is starting corner Tramaine Brock. San Francisco invested eight draft picks in the secondary over the last three drafts.

General manager Trent Baalke has stacked the deck against the 49ers wide receivers. Outside of Smith, none of them have proven to be a credible threat to defenses, so coordinators will feel comfortable allowing their cornerbacks to cover them one-on-one.

Despite their struggles, there is room for hope that come Week 1. Kelly’s track record with offenses means the 49ers’ offense is in far more capable hands than former coordinator Geep Chryst’s, who called the plays for the 31st-ranked offense in 2015.

That isn’t much of a bar. Kelly fielded a top-10 attack in two of three seasons with the Philadelphia Eagles. As Kaepernick and Gabbert find their offensive rhythm, the 49ers receivers should follow suit.

“I would say typically the defense has the advantage when you start because you’re not game planning for what they are doing,” quarterback Colin Kaepernick said. “So they might give you looks that you don’t necessarily install for until you get into a game week.”

Kelly’s up-tempo offense in Philadelphia featured three-receiver sets almost 70 percent of the time. No matter how the depth chart unfolds, it’s inevitable young players will be forced into the spotlight. In the meantime, the 49ers secondary is more than happy to ensure that they are properly tested throughout training camp.

After all, diamonds are formed in high-temperature, high-pressure conditions, and if one is to emerge from the 49ers wide receiving corps, it will be because the 49ers cornerbacks applied the necessary ingredients.