Mac Jones looked locked in from the first snap, carving up the Rams defense with ease. He went 15-of-23 for 179 yards and two touchdowns in the opening half. That kind of rhythm had San Francisco rolling with a 17-7 lead. Fans in red and gold were loud in SoFi Stadium. But then the energy flipped as Jones went down.

NFL insider Ian Rapoport broke it down: “#49ers QB Mac Jones, playing through a PCL sprain (originally from training camp) and wearing a bulky brace, goes down hard, grabbing his knee in a lot of pain.” That was enough to silence the visiting cheers.

And yes, the play that flipped the script was a brutal blind-side hit. Jones took the shot from Rams linebacker Byron Young on third-and-goal midway through the third quarter. The 27-year-old immediately clutched his knee on the turf. He already had a brace strapped tight, so seeing him down made it worse.

However, he got up and jogged off the field during the commercial break. That gave the Faithful some relief, but the scene had already shifted the momentum inside the stadium.

Jones has been filling in for Brock Purdy, who is sidelined with a turf toe injury. Jones himself has been playing through a sprained left PCL, with a brace on that knee every snap. This was his third straight start, but the depth behind him is thin. The only other option?

Adrian Martinez, a young quarterback fresh off the Jets’ practice squad who has never thrown an NFL pass. That is not the insurance the red and gold wanted to rely on.

Finally, a sideline update calmed things down, at least a little.

Prime Video sideline reporter Kaylee Hartung said that Jones was sitting on the bench, receiving fluids from the 49ers’ training staff. He was receiving treatment to his calf, suggesting that he might have been dealing with a cramp.

“The athletic trainer was using a massage gun on his left calf. I didn’t see any kind of formal evaluation of that knee. All of that suggests he was cramping,” Hartung said. However, the QB’s incident also sparked a debate among analysts.

Analysts question officials after Mac Jones incident

The Rams should have been flagged for the hit that left Mac Jones shaken, at least according to Thursday Night Football rules analyst Terry Michael. On the broadcast, he didn’t hold back. “I think it’s roughing the passer, Kirk [Herbstreit], I think [Young] lands on [Jones] with full body weight right there,” McAuley said as the reply rolled.

He doubled down too, adding, “That should have been roughing the passer.” For 49ers fans inside SoFi Stadium, the moment Jones hit the turf, it felt like an obvious missed call.

Now, this isn’t a new wrinkle in the rulebook.

The “body weight” clause has been there since 2018, when the league cracked down after former Vikings linebacker Aaron Barr dropped Aaron Rodgers and broke his collarbone. Since then, defenders have been warned repeatedly-don’t drive through the QB and land their full weight. Yet here we are again, with a quarterback on the ground and no flag in sight.

For the 49ers, the non-call stung. It likely cost them a shot at the end zone, since a penalty would have placed them on the one with new downs. If the Rams steal the win, the missed flag will be the headline. For now, though, the red and gold are just thankful their quarterback walked away from it.