It turns out Shanahan was upset that Seahawks quarterback Russell Wilson had thrown Fred Warner's shoe, which delayed the 49ers as the rookie linebacker tried to recover it. Shanahan said the penalty was the "icing on the cake" and the "tipping point" for him.
"It was definitely a number of other [questionable calls] from earlier that was a build up," he added.
Shanahan made it a point to state that he doesn't know if Wilson's actions were malicious but only that it created an unusual situation.
RELATED
Defensive tackle DeForest Buckner was on the field for the 49ers at the time and witnessed what television cameras failed to catch. He joined KNBR on Wednesday morning and described the situation from his perspective.
"It was on the play where the sack that should have been counted but (the refs) counted us offsides," Buckner said on the "Murph & Mac" show. "Fred's shoe came off and [Wilson] grabbed his shoe and chucked it like 10 yards behind their line of scrimmage. He made his whole offense get on the ball and snap the ball real quick.
"We didn't have enough guys on the field. We had guys trying to run on the field for Fred, and we got called for offsides or something like that. It should have been a dead ball. The referees should have called it."
Buckner does admit that fans and the local media probably would have praised quarterback Nick Mullens had he done the same thing.
You can listen to the entire conversation with Buckner below.
More San Francisco 49ers News
-
49ers teammate on Fred Warner: 'Best football player I've ever been on the field with'
San Francisco 49ers linebacker Fred Warner showed no lingering effects from the ankle injury that limited him to just six games last season. The All-Pro defender was his usual dominant self in the 49ers' 27-7 Week 1 win over the Los Angeles Rams in Melbourne, Australia. Warner... -
49ers Notebook: Fred Warner reflects on 'dream' reunion, Jaden Dugger's debut; Christian McCaffrey misses party
San Francisco 49ers linebacker Fred Warner played with his usual high energy in Week 1's victory over the Los Angeles Rams in Melbourne, Australia. That should come as no surprise, as the All-Pro defender is widely regarded as the NFL's top linebacker. Warner finished with a... -
49ers legend Patrick Willis reacts to Fred Warner breaking his tackle record
San Francisco 49ers linebacker Fred Warner recorded a game-high 11 tackles last week against the Los Angeles Rams, bringing his career total to 959, according to Pro Football Reference. That moved him past Hall of Fame linebacker Patrick Willis, who finished his career with 950... -
49ers game changers: Trent Williams on Kaelon Black, Nick Bosa, Fred Warner
San Francisco 49ers rookie running back Kaelon Black shared this week what it is like to play alongside offensive tackle Trent Williams, a sure-fire future Hall of Famer. "Growing up, I was a Washington fan, so he was on Washington," Black said. "I was like in third, fourth...