The Arizona Cardinals had planned a party for 2018 NFL draft, and thousands of party guests were in for a surprise.

The Great Lawn across from University of Phoenix Stadium in Glendale was buzzing with excitement on Thursday, as a crowd of red and white jerseys awaited the Cardinals' slotted 15th pick.

But as soon as the broadcast announced that the Cardinals traded up for the 10th pick of the draft, the Red Sea became electric.

"Me and my buddy, we were talking and we were wondering if we were going to trade up or not," said Nicholas Westfall, who was in the front row.

"We'd been hoping all offseason that was going to happen, and once we saw the red banners in the back, we knew it was on."

Cardinals flag bearers had paraded to the back. The cheerleaders took the stage. Big Red began to dance. The excitement on the lawn swelled as the Jumbotron cut to the Cardinals' headquarters.

Fans pulled out their phones to capture the moment. Alvaro Sierra started a "Q-B, Q-B!" chant. The volume for a moment simmered as fans read on screen that the pick was in.

When Roger Goodell announced that the Cardinals had selected UCLA quarterback Josh Rosen, they erupted.

"The Red Sea has Rosen!" Sierra shouted.

The energy was palpable. Fans jumped up and down, all cheering for their new quarterback.

"I am so excited right now. We've got the future going on," Westfall said.

Early on, the fans on the Great Lawn seemed to be pulling for a quarterback. When the Cleveland Browns took Baker Mayfield with the first pick, they brought about a chorus of groans and numerous boos in Glendale. However, when the New York Giants took Saquon Barkley at No. 2, the crowd's reaction was more mixed. Cheering outweighed anything else.

The crowd was fairly tame until the trade happened. After that, they were giddy all night.

"I love it. We needed a quarterback, and we got one," said Sherri Burris, who was watching alongside her mother. Both have been season-ticker holders for at least 10 years.

They got their quarterback, and they got to hear from him as well. Rosen would address the crowd over satellite, sporting a "Rise Up Red Sea" cap.

"When he did that, he made me feel a part of it, like he was talking to me. So I felt very enthusiastic about that," said Kaygee Hernandez, sitting in the front row of picnic tables.

Rosen was candid with fans, saying he was surprised he dropped to the 10th pick, having felt he was better than that, but that he was excited to head to Arizona.

That confidence sat well with the Cardinals fans, who hung on to every word, cheering only between Rosen's answers.

"I know that he is an incredibly intelligent guy," said Pamela Watson, who was on her feet and waving her arms as Rosen spoke. "I think he’s got a lot of self-confidence, but I don’t think he’s too cocky. I’m just very excited to have him. I know he’ll be an amazing asset for us."

Cardinals General Manager Steve Keim and President Michael Bidwill addressed the fans, as well.

"You ought to be excited, because this is our quarterback of the future," Bidwill told fans.

Though the Rosen pick came just after 6 p.m., most fans stayed until the very end. There was a zip line, a virtual reality area and a tent where Cardinals players signed autographs.

There was the promise of fireworks to come, but also a true curiosity about where Louisville quarterback Lamar Jackson would wind up.

When Jackson was taken by the Baltimore Ravens who had traded for the last pick of the first round, the crowd erupted into cheers one more.

Gates to the lawn had opened at 4:30 p.m., but some fans, like Hernandez, arrived as early as 3 p.m. to snag front row seats.

"I wanted to get this experience. My son’s out there – that’s the first time he’s ever been there," he said. "I wanted to make this something memorable for him and his family in the future."

For Hernandez, the new family tradition was made better by the Rosen pick.

"I thought it was a shocker," he said. "I didn’t think we were going to get something this great. I want to be part of it, I want to be part of that future."

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