As fans gathered inside Oakland Coliseum for Opening Day on Thursday, thousands more stood in the parking in protest of the Oakland Athletics' ownership.

Per ESPN's Tim Keown, fans waved "sell" flags while eating free tacos and enjoying live music, staying in the parking lot during Oakland's matchup with the Cleveland Guardians.

The announced attendance for the game was 13,522—about 21 percent of Oakland Coliseum's capacity.

The protest, which is part of what fans are reportedly calling "Summer of Boycott," comes as the A's begin what could be their final season in Oakland. Major league owners voted unanimously to approve the A's move to Las Vegas, the club's lease with the Coliseum is up after this season and the team's ownership is targeting a 2028 opening for a new stadium in Nevada.

Among the fan groups in the parking lot in Oakland on Thursday was an organization called Schools Over Stadiums, which is a political action committee of the Nevada State Education Association attempting to get a referendum on the ballot to stop the allocation of $380 million in public funding to help A's owner John Fisher.

Last season, fans took a different approach to protesting. Rather than missing games, fans showed up to the stadium in two "Reverse Boycott" games led by fan groups Oakland 68s and Last Dive Bar. With the move to Las Vegas approved, fans are now taking a different approach.

In anticipation of protests outside the stadium, the A's have opted to keep the parking lot closed until two hours before the game, per ABC News' Tara Campbell. Whether that move from the A's will work is to be determined, but for now fans will continue to make a stand.