OAKLAND (TNS) — Chris Harris Jr. lay on the ground, keeled over in pain as Broncos trainers rushed the field. As he slowly turned on his back and then stood up, Harris summoned the referee and told him Oakland receiver Michael Crabtree sucker punched him in his gut.

And that's when all hell broke loose here Sunday.

Denver cornerback Aqib Talib got into it with Crabtree on the next play, spurring a full-on brawl along the Broncos' sideline with punches thrown, a helmet tossed and another chain snatched by Talib. Harris returned to the game soon after, but Talib, Crabtree and Raiders guard Gabe Jackson were all ejected after the brawl and left the field to a chorus of boos.

Soft, these Broncos weren't Sunday. But in a road game in which they desperately needed a win, the Broncos instead lost for a seventh consecutive time, 21-14, notching another embarrassing mark on their troubled season. And, they were forced to switch quarterbacks yet again.

Paxton Lynch, who took his third career start Sunday, left with an ankle injury in the third quarter and was replaced by Trevor Siemian, who kept the Broncos in it late with two touchdown passes. One more defensive stop and the Broncos had a chance to tie it up in the closing minutes.

But the debacle of the first three quarters did them in. The Broncos left California with three of their defensive starters either ejected or hurt, and their quarterback, Paxton Lynch, in a walking boot.

If there was one sequence to fully encapsulate their season it happened at the start of the second quarter. Lynch — the Broncos' third starting quarterback this season — guided them to the 1-yard line. But on a second-and-1, he rolled left, and threw across his body to tight end Virgil Green, who was blanketed. The ball bounced off the hands of Green, and after another tip ended up in the arms of Oakland linebacker NaVorro Bowman.

The interception was the first for the Raiders this season, and they made good use of it. On the ensuring drive, quarterback Derek Carr spotted Amari Cooper for a 9-yard touchdown against rookie cornerback Brendan Langley — who was in the game because Talib was ejected.

These are the Broncos of 2017, without a true starting quarterback, without a win in nearly two months, with tempers building and without a clear plan to fix the mess.

Amid the madness of the opening quarter, Broncos defensive end Derek Wolfe was carted off with a neck injury and ruled out for the remainder of the game.

And amid the rough play throughout the game, the Raiders lost two of their top targets. Cooper was crushed on a hit by safety Darian Stewart in the second quarter. Stewart was flagged for unnecessary roughness and will likely have to pay a hefty fine to the league. Cooper was later ruled out with a concussion, but his 12-yard catch wasn't for naught. Marshawn Lynch trotted into the end zone less than two minutes later to give Oakland a 14-0 lead. Then in the third, running back Jalen Richard expanded their lead to 21-0 with a 6-yard touchdown catch.

The snowball effect that has plagued the Broncos all season was in full force. One early issue led to another and another until the game spun out of their control — along with their season.

The Broncos' first half was a scripted nightmare as they were shut out, lost two defensive starters and watched Paxton Lynch complete only half of his passes for a 16.7 passing rating.

But the horrors would continue, and get worse before they could get better. Nose tackle Domata Peko was lost to a knee injury, and a teary-eyed Lynch later hobbled to the sideline in pain.

Lynch entered with only two NFL starts to his name, so perfect wasn't expected. But efficiency certainly was, and the Broncos got anything but. In less than three quarters of play, Lynch took four sacks and went 9-of-14 passing for 41 yards, an interception and a 38.4 passer rating before leaving with an ankle injury. He came up lame after a pass play on third down and was immediately ruled out and replaced by Siemian, the team's starter to open the season.

"I thought I played pretty well. There were some plays I had an opportunity to make and I made," Lynch said. "There were also some plays that I just missed. But this was the first that I had played with all these guys in a while, so it felt good to get out there and play with them. But obviously, this isn't the result that we all wanted."

Siemian promptly engineered a 10-play, 93-yard drive in only three minutes, 48 seconds that ended on a fourth-and-6. Siemian launched a 25-yard strike to Cody Latimer in the corner of the end zone, sparing Denver another shutout loss and injecting some life into the offense.

Although he nearly picked off twice on his next drive, Siemian took the Broncos 60 yards in only 3:07, finding Bennie Fowler for the 25-yard strike in the end zone.

Suddenly the Broncos were within one score of tying the game. But the Raiders quickly quashed any remaining hope Denver may have had as Carr found receiver Cordarrelle Patterson for a long completion, then ate up the rest of the clock.

In his short time on the field, Siemian went 11-of-21 for 149 yards, two touchdowns and 107 passer rating. But it may not be the last time under center. The Broncos' season is cooked. But their quarterback carousel continues to spin, round and round.