Two flags flutter behind the outfield wall of Alumni Field. One is the stars and stripes of the United States. Below it is a smaller maize and blue block ‘M.’ The two flags billowed in a strong breeze on Friday afternoon, a wind that helped the Michigan softball team turn a tight game against Michigan State into a blowout.

For an inning and a half, the Wolverines’ 21-2 win over Michigan State epitomized the classic in-state rivalry. The second-place Spartans (7-4 Big Ten, 21-17 overall) jumped all over sophomore pitcher Haylie Wagner, working a walk before lining a double down the left-field line and scoring a run on a wild pitch. The conference-leading and 12th-ranked Wolverines (12-0, 35-7) threatened in the bottom half of the frame, putting runners on second and third with only one out, but they failed to bring a runner home.

But when freshman phenom Sierra Romero — who boasts a .416 batting average and 15 home runs on the season — stepped up to the plate, the winds showed signs of change. The two flags in centerfield started fluttering in the brisk breeze.

From the crack of the bat, the crowd knew it was gone and that the shortstop would trot around all four bases and into a mob of teammates at home plate. Romero smashed a bomb to deep left center, with a little help from the wind. Michigan State’s left fielder Alyssa McBride had no chance. She just turned to watch the ball sail over the wall, over a tent and into a grove of pine trees that divides Alumni Field from Ray Fisher Stadium. With the grand slam, the rout was on.

The awe of Romero’s blast didn’t last long. After a quick inning by Wagner, sophomore catcher Lauren Sweet launched a shot that almost hit the pole holding those two flags. Then, the wind caught junior centerfielder Lyndsay Doyle’s sharp line drive just enough, and it clanged into the fence inches above the home-run line.

Freshman pinch hitter Kelsey Susalla followed with a rocket over the right field bleachers, something that Michigan coach Carol Hutchins had never seen in her 29 years with the program. Not to be outdone, junior Taylor Hasselbach belted a moonshot that cleared the outfield wall of both Alumni Field and Ray Fisher Stadium, momentarily interrupting a baseball game.

“We were definitely firing on all cylinders on offense,” Hutchins said. “The wind was blowing out and you have to adjust your game. The key is that we’re swinging well and seeing the ball. You can’t always control everything else.”

The Wolverines scored 13 runs in the third inning, and they still weren’t done.

Michigan finished the contest by setting the mark for runs tallied against the Spartans, scoring 20 runs for the first time since 2000. The last of the six home runs meant the most to Hutchins, as junior Katie Luetkens rounded the bases with a fist pump and a smile after lining a two-run pinch-hit drive over the fence — just her second career hit.

“It was a great feeling, a lot of emotion,” Luetkens said. “Lots of people want that moment, and I got the opportunity to have it. That’s something I can cherish forever.”

Michigan and Michigan State will play the final two games of the series this weekend in East Lansing, but if the wind blows out at Secchia Stadium, it might not be a home-field advantage for the Spartans at all.