The Nationals are taking up the fight after mass killings in Buffalo and Uvalde.
75 professional teams are anticipated to participate in "Wear Orange Weekend" to campaign for gun regulation, according to Everytown for Gun Safety.
While far from the 180 professional teams in baseball, football, basketball, hockey, and soccer, it's up from last year's 29. Players often wear an orange ribbon.
Teams can also join other U.S. gun-control groups.
"Unprecedented. It's crucial "Angela Ferrell-Zabala, Everytown for Gun Safety's movement builder.
"They're meeting their market, the moment"
An 18-year-old gunman massacred 19 elementary school children and two instructors with an AR-15 last month in Uvalde, days after a white supremacist slaughtered 10 people at a supermarket in Buffalo, New York.
The shootings reignited calls for Congress to curtail gun violence, but many Republicans said they'll reject gun restrictions.
A Reuters/Ipsos poll last month found that 63% of Americans, including 53% of Republicans, support moderate or strong gun laws.
This year, the Nationals, Texans, and Spurs are teaming with Everytown for Gun Safety. The organisation didn't include all participating franchises.
The Nationals wore "enough" T-shirts before Friday's away game in Cincinnati, joining six other D.C.-area teams to "demand for an increased commitment to reducing gun violence."
The move occurred a week after the Yankees and Rays posted gun violence information instead of game coverage.
The Toronto Raptors petitioned Canadian lawmakers Friday to observe the first Friday of June as National Gun Violence Awareness Day.
Steve Kerr skipped a pregame press conference to call for tougher gun regulation.
On Friday, the WNBPA announced a fourth year of partnership with Everytown.
"Risky? Yes. Fans can be isolated. You can anger management, sponsors, "Amy Bass, a Manhattanville College professor who analyses sports, society, and politics.
You can also empower your fanbase.
Bass called the Summer of 2020 Black Lives Matter activism a "spark" for athletes and teams.
She asserted Summer 2020 introduced sports.
Coco Gauff and Naomi Osaka brought the Black Lives Movement to the global scene through tennis two years ago.
"We hold these athletes in great regard, but they're also community members," said Ferrell-Zabala. "It's normal for them to use their voices to investigate this issue."