The W.N.B.A. begins its 27th season on Friday with new rules, new rosters and one big return. Here’s what to expect.

After nearly 10 months in detention in Russia, Brittney Griner is playing basketball again.

Griner’s detention clouded the W.N.B.A. season last year. She was arrested at an airport near Moscow on drug charges in February 2022, and subsequently convicted and sentenced to nine years in a penal colony. The league regularly paid tribute to her during the season, and her fellow players spoke out on her behalf.

Griner was released in a prisoner swap in December, and after time spent recovering privately, she signed a one-year contract to return to the Phoenix Mercury.

Griner played no basketball during her imprisonment and is still working to get back into game shape. “Everybody tells me to give myself grace and that it’s going to take time,” she said at a news conference in April, “but that’s the hardest thing to do for a pro athlete because we always want to be right back at our top shape.”

Griner and the Mercury open their season on Friday in Los Angeles against the Sparks.

The off-season was dominated by free-agent signings and trades that established what could be two superteams: the Liberty and the Las Vegas Aces.

The Liberty made three key moves: First, they traded with the Connecticut Sun for Jonquel Jones, the league’s most valuable player in 2021. Then they landed one of the top free agents: Breanna Stewart, the 2018 M.V.P., who had won two championships in Seattle. Finally, they signed the league’s active assists leader, Courtney Vandersloot. Those three join the returnees Betnijah Laney and Sabrina Ionescu, who have each made an All-Star team.

The reigning champion Aces already featured an impressive collection of talent: last year’s M.V.P., A’ja Wilson (who also won in 2020); Chelsea Gray, the 2022 finals M.V.P.; and their fellow All-Stars, Jackie Young and Kelsey Plum. And then they went and signed Candace Parker, the two-time M.V.P., two-time champion and seven-time All-Star. They also picked up the veteran Alysha Clark, who won two titles with Seattle.

The rest of the league isn’t backing down from the superteams. “In the best movies, the underdog ends up on top,” Elena Delle Donne of the Washington Mystics told reporters this month.

But still, the Aces and Liberty are far and away the betting favorites to win it all.

Some of the newest W.N.B.A. players are just weeks removed from finishing their college careers. How they make that transition will be crucial to the fortunes of their new teams.

Aliyah Boston was the obvious choice of the Indiana Fever as the No. 1 overall pick in the April draft. Boston, who led South Carolina to a national title in 2022 and back to the Final Four this year, is expected to be a franchise cornerstone for the Fever as they rebuild. Though the competition she faces will be tougher in the W.N.B.A., Boston should be able to score more easily without facing the same double and triple teams she saw in college.

With this year’s No. 2 pick, Minnesota drafted Diamond Miller, who led Maryland with nearly 20 points a game in the 2022-23 season. Miller is a versatile and athletic wing who should pair well with Napheesa Collier.

Haley Jones, the No. 6 pick in the draft, was a leader for four years at Stanford, including the Cardinals’ 2021 title run. She slots in well on an Atlanta Dream team looking for more playmakers.

The league also updated its rule book this off-season.

W.N.B.A. coaches will now be able to challenge one — and only one — call per game. Coaches can ask for reviews on three kinds of calls: a foul called on their team, an out-of-bounds call, or a violation for goaltending or basket interference. Coaches will be limited to one challenge even if the challenge is successful, and even if the game goes to overtime.

Officials may also now penalize players for committing a foul during a fast break without making a legitimate play on the ball. For this, a transition take foul, the offensive team will be awarded one free throw, which can be taken by any player on the floor, and the offensive team will keep control of the ball.

The W.N.B.A. also has new guidelines governing sideline behavior. In an effort to limit disruptions and distractions, the league is telling players who are not in the game that they may not stand “for a prolonged period.” Players and coaches are also prohibited from “attempting to distract their opponents in an unsportsmanlike manner.” Teams could receive a delay-of-game warning or a technical foul for a violation.