Spectators rushed the field to stage a climate change protest at halftime of Saturday's Harvard-Yale game, delaying the start of the second half by nearly an hour and causing the game to finish in near-darkness.

The 136th edition of The Game between the Ivy League rivals went to halftime around 1:40 p.m. ET, and students from both schools occupied midfield after the Yale band finished performing.

Most protesters left after about an hour when they were escorted off by police, who then told about two dozen who remained they were under arrest. The field was ultimately cleared, and the game resumed at 2:48 p.m. ET.

However, the delay led to an issue for the game's finish because the Yale Bowl lacks stadium lights, and sunset in New Haven, Connecticut, was set for 4:26 p.m. on Saturday.

The darkness problem was compounded as the game went to double overtime, but Yale ultimately got a stop to win 50-43 -- and secure a share of the Ivy League title -- at 4:38 p.m., before it became too dark to play.

In a statement, the Ivy League referred to the protest as "regrettable." Yale said that while it "stands firmly for the right to free expression," it had issues with how the protesters went about their demonstration.

"The exercise of free expression on campus is subject to general conditions, and we do not allow disruption of university events," Yale said in its own statement.

Protesters were on the field at Yale Bowl for nearly an hour and delayed the start of the second half. AP Photo/Jimmy Golen

Yale coach Tony Reno said the unusual interruption was an example of what has made his university's rivalry with Harvard stand the test of time.

"It's what makes Yale Yale," Reno said. "Our group, I'm sure if you asked them and the Harvard guys what makes it special, it's not only the game of football. It's the passions."

Players were stretching and warming up when the protesters first took the field. Police in yellow vests lined up alongside the sit-in but did not intervene. When the 15-minute halftime expired and the protest continued, the players returned to the locker room as dozens more fans streamed onto the field to join in. Fans remaining in the stands began to boo, but only briefly.

The public-address announcer implored the group to leave, repeating, "As a courtesy to both teams, the game must resume." Protesters responded by chanting, "OK, boomer."

Yale police Chief Ronnell Higgins spoke to the protesters over a megaphone, trying to convince them that they had made their point but it would be lost if the situation escalated.

Some protesters held banners asking their universities to act on climate change and Puerto Rico debt relief, including one sign that read, "Nobody wins. Yale & Harvard are complicit in climate injustice." Another read, "This is an emergency."

"Hey, hey, ho, ho, fossil fuels have got to go," some protesters chanted.

Some protesters had tied themselves together and were requesting police to arrest them, according to reporting by ESPN's Jack Ford. After about an hour, police formed a line and moved forward from the Yale sideline toward the Harvard sideline. A protest leader encouraged all "internationals" to leave. An agreement was reached to escort those remaining off, with one police officer to every two protesters.

Those who did not leave then were informed by Higgins that they would be arrested. Between 20 and 30 protesters were arrested, according to protest organizers.

Rachel Sadoff, a junior at Harvard, said about 150 students from the two universities planned to participate in the protest. She said about 100 more students who had been sitting in the stands joined in, and that those arrested were released and given a court date.

Caleb Schwartz, a Harvard student and spokesman for the group Divest Harvard, said Saturday's protest was the result of months of coordination.

"This is a very deliberate choice of targeting this specific [game] to get our action out there," Schwartz told ESPN's Paul Kix.

Information from The Associated Press was used in this report.