In an Instagram post after the incident, Ramona Saavedra identified her fiancé as Ricardo Juarez.
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"Tad bit extreme," Saavedra wrote. "But he's a LEO. What can you expect. And of course I said YES!"
The footage shows the man, wearing a Dodger hat and hooded sweatshirt, bending down on one knee after making his way onto the field during the seventh-inning stretch. He is taken to the ground by a security guard in a running tackle and then escorted off the field. Fans in the stands -- many of them recording videos with their cellphones -- continue to cheer.
A photo posted by Saavedra on social media shows her and Juarez smiling as she shows off the engagement ring on her finger.
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Saavedra and Juarez did not immediately respond to ABC7's request for comment. A Dodgers spokesperson said the team's front office had no comment on the proposal or the tackle.
Whether Juarez was cited or arrested by police was unclear.
Will Smith went 3 for 5 and drove in three runs, James Outman homered and the Dodgers defeated the Diamondbacks 8-2 in their season opener.
Julio Urías, last year's National League ERA leader at 2.16, got the victory in his first career opening-day start. The left-hander allowed four hits and two runs in six innings. He struck out six.
ESPN contributed to this report.