Kurtenbach: Trey Lance or Sam Darnold for 49ers backup QB? Kyle Shanahan says ‘why not both?’

The battle for the backup quarterback job between Trey Lance and Sam Darnold turned out not to be much of a battle at all.

SANTA CLARA — The defining storyline of the 49ers’ preseason won’t be defined anytime soon.

For weeks, the battle between Sam Darnold and Trey Lance to be the 49ers’ No. 2 quarterback has dominated the discourse around the team. Who will be Brock Purdy’s top backup — the former No. 3 overall pick the Niners selected in 2021, or the former No. 3 overall pick they signed as a free agent this past spring?

Two preseason games have hinted that Darnold might be the man for the gig, but Lance hasn’t fully disqualified himself yet. Friday’s preseason finale was angling to become the final and most important showdown of this gripping conflict.

Then Kyle Shanahan spoke on Tuesday.

The 49ers’ coach poured cold, pragmatic water on top of this red-hot battle to sit on the bench when he suggested that both quarterbacks will be carried on the team’s roster this regular season.

On top of that, he said that they could easily swap places week by week.

Yes, the No. 2 in Week 1 might not be the same for Week 2.

Worse yet, as the public portion of the preseason ends — Wednesday is the season’s last practice fully open to media — the battle to be No. 2 will continue behind closed doors.

The fun is over, folks.

I can’t say we learned much.

Of course, while Shanahan is ruining our fun, it should be noted that he and the Niners are wise to keep both quarterbacks. Reasonable people can disagree on if the 49ers should trade Lance, but that’s merely hypothetical. In reality, there’s not much of a trade market for Darnold or Lance forcing Shanahan’s hand.

Plus, this team is acutely aware of how important quarterback depth is.

In fact, this team is also why keeping two backups is reasonable. In light of Purdy’s injury in last season’s NFC Championship Game, the league reinstalled the “emergency” third quarterback for this season.

That means the Niners (and every other team) can have three quarterbacks in uniform for every game, with only two counting on the game-day roster.

This ridiculous, sanctioned loophole is called the “Brock Purdy rule” around the league.

By the end of this season, it might be named after Lance or Darnold.

Shanahan ideally carries two quarterbacks on his roster, but he has made exceptions with the Niners, even without rulebook help.

Last season, the Niners carried Purdy on the 53-man roster after the former last pick of the draft’s impressive preseason. With Lance (the starter) and Jimmy Garoppolo (the backup), keeping Purdy meant only carrying nine defensive linemen at the start of the season. The Niners managed, and keeping Purdy proved to be one of the great decisions in franchise history.

Before that, Shanahan kept C.J. Beathard and Nick Mullens on the roster as backups to Garoppolo. That decision does not carry much historical weight.

We’ll see how this Lance and Darnold decision looks in a few months.

Here’s how I expect this to all play between now and then:

• The Niners will cut or trade (for next to nothing) Brandon Allen before Aug. 29. I’d like to think the guy didn’t lose his opportunity to make the roster because he left the team to be with his wife while she gave birth, but, well, his timing wasn’t great. The former No. 2 quarterback in Cincinnati impressed in practice and the Niners’ preseason opener, but ultimately ran out of snaps right around the same time he left the team for a few days.

“It’s just hard to play four guys,” Shanahan said. “We got him a lot earlier in camp knowing that, especially when we had more threes. But, we don’t even do threes now. Our ones are consisted of ones and twos, and our twos are consisted of twos and threes.”

• Both Lance and Darnold will make the 53-man roster.

• Lance will be listed as the No. 2 quarterback on the depth chart ahead of the Niners’ season opener. Why make waves if the number doesn’t mean anything?

• With both Lance and Darnold in uniform every game, Shanahan will use both throughout the season. If the Niners are up big and want to run out the clock, Lance will see much-needed playing time. If Purdy gets injured and the Niners need a quarterback who can come in and win them a game, I bet Shanahan turns to Darnold.

• Trade values for both quarterbacks never increase enough throughout the season to where the Niners trade one away.

Now, will any of this be fun?

Not really.

But the Niners aren’t interested in side-story entertainment. They’re trying to win a Super Bowl.

And a big part of that is ensuring they don’t run out of quarterbacks again.

I can’t help but think that all of this hype around the backup quarterback job was another dose of Shanahan misdirection:

Nick Bosa isn’t with the team. The defense has a new coordinator. The team’s new right tackle hasn’t impressed. Purdy isn’t even throwing every day.

But during training camp, the top story, day in, day out, is how the backup quarterbacks did in practice.

Yes, Shanahan played us all like a Packers’ linebacker.

Now can we start the season already?