Back in June, the 49ers’ mandatory minicamp felt more like quarterback target practice – for the defense. Brock Purdy threw three interceptions in live drills. Most of them looked like bad decisions. But Kyle Shanahan didn’t see it that way. “I thought it was good,” he said, shrugging off the stat sheet everyone else was obsessing over. To him, June was the time to miss throws, take risks, and let quarterbacks rip before the games count.

It’s a philosophy he preaches. Learn from mistakes now, so you’re not blindsided later. “You go through all these practices and you never throw a pick, you’re probably not getting better,” Kyle Shanahan explained. The QB room took that to heart this summer – especially Mac Jones, who arrived in March looking for a reset after his Patriots and Jaguars stints went south. The 26-year-old wanted to learn from Purdy’s reps as much as his own. But fast-forward to August, and the ‘learning’ phase is starting to look more like a roster decision Shanahan might already regret.

According to Insider Grant Cohn of Sports Illustrated’s 49ers, Aug. 9, the preseason opener against the Broncos was a lowlight reel for Purdy’s backups. Jones at least opened with a perfect 50-yard deep shot to Jordan Watkins. But then protection collapsed, Watkins ran the wrong route, and Jones’ night ended with an interception on third-and-nine. Carter Bradley and Tanner Mordecai? Cohn described it as “a competition to see who could play worse.” Both threw picks, but Mordecai added a fumble for good measure. His conclusion: “neither should make the team.”

For Jones, this isn’t just another rough preseason night. It’s the latest in a two-year stretch where every chance to regain footing has slipped away. His first media session as a Niner back in June included an admission: he’d been “a little bit shaky” and felt like he was “drinking from a (fire) hose” learning Shanahan’s system. Even in practice, he’s been prone to off-target throws and hesitation – the exact habits he vowed to break. Aug. 9 was a reminder that in Shanahan’s world, backup quarterbacks aren’t just clipboard holders. They’re one Purdy injury away from being the offense.

That’s why Shanahan may now make changes to Purdy’s QB room. That doesn’t mean demoting Purdy. It means rethinking who sits behind him, who gets reps, and whether an outsider needs to be brought in before Week 1. The depth chart right now feels like a Jenga tower with a few too many pieces pulled out. Preseason is supposed to be the testing ground. Instead, it’s exposed a depth problem that could force Shanahan’s hand sooner rather than later.

Kyle Shanahan’s backup plan blows up in Denver

The scoreboard told a simple story: Broncos 30, 49ers 9. But the game itself was even uglier. San Francisco actually led 9-0 in the first quarter before the offense disappeared. Denver then outperformed them in every major offensive category. And while most starters sat out, Shanahan didn’t sound like a coach comforted by that detail. “It was frustrating,” he said bluntly. 

The QB numbers didn’t help: Jones went 4-of-7 for 74 yards with an interception and two sacks. Bradley managed 6-of-14 for 32 yards and a pick. Mordecai – signed just two days earlier – went 3-of-6 for 21 yards, an interception, and a sack. It’s preseason, sure. But Kyle Shanahan’s offense is built on timing and rhythm. None of that was on display.

The good news is there’s still time to fix it. The 49ers head to Las Vegas on Aug. 17 for a preseason matchup against the Raiders. For Shanahan, it’s another chance to see if anyone in Purdy’s QB room can prove they belong. But after Denver, those seats aren’t just up for grabs –  they’re hanging by a thread.