Marvin Bagley III makes an impact while playing among the pros in Drew Summer League

They surrounded Marvin Bagley III as if he were already an NBA All-Star. Fans armed with cellphones, sharpies, basketballs and T-shirts wanted autographs and photos with the player who has been the talk of the Drew League this summer.

Bagley is a teenager whose senior year in high school should be starting in a couple of weeks, but recently he’s gone against the likes of NBA star DeMar DeRozan and played on the same team with James Harden and Chris Paul.

On Wednesday night, with a crowd of 1,500 filling the Los Angeles Southwest College gymnasium to watch a special game between Los Angeles and Seattle teams featuring current and former professional players, Bagley finished with 18 points and 20 rebounds.

“It’s been great for me,” Bagley said afterward. “It’s just been fun. It’s a lot more competition. Guys are stronger. Everybody wants to win, so you have to come out every game with your best performance and try to get a ‘W.’”

Bagley played for Chatsworth Sierra Canyon High last season but reportedly wants to join a college team this fall.

His father, Marvin Jr., was asked about the family’s plans but didn’t offer much insight. “We’re taking it day by day,” he said, “looking at the best options.”

Duke, USC and UCLA appear to be the schools Bagley is giving the most consideration, assuming he can fulfill NCAA requirements to play.

Of course, if the NBA allowed high school players to enter its draft again, Bagley’s decision would be a no-brainer.

There have been a few high school players before who played against the pros in the Drew League, including DeRozan, but none has shown as well as Bagley.

“Oh my gosh,” said Mike McCaa, the chief financial officer of the Drew League. “In 44 years, he’s had the most impact of any high school player I’ve witnessed. He plays well above his age level and has a very strong sense of maturity.”

Bagley, who is listed at 6 feet 11, 220 pounds, appears to be more mobile and in even better shape than he was in earning recognition as the state player of the year while leading Sierra Canyon to a 27-3 record last season.

He runs the court with a sense of urgency and isn’t afraid to mix it up inside with physical grown men. Naturally a post player, he can step outside and make jump shots. He also blocks out for rebounds and executes the pick-and-roll like a veteran.

“He understands he has to bring it every night, every play,” his father said. “This isn’t high school. It’s quite an experience.”

At 18, Bagley is showing he’s more than up to the task of lights, cameras and fans focused on him.

“He’s so comfortable on the floor,” McCaa said. “This kid is totally unfazed by the level of competition.”

Keion Kindred coached Bagley against Seattle, a team coached by former Clippers guard Jamal Crawford.

“He’s a pro,” Kindred said. “He has unbelievable composure around pro players, which is unbelievable for a high school player. He doesn’t say much, plays hard and accepts the challenge.”

On Wednesday, former NBA All-Star Baron Davis, 38, kept looking for Bagley — as if he was seeking to feed the ball to Tim Duncan or Shaquille O’Neal.

One reason the pros like playing with Bagley is that he doesn’t take plays off. He’s shown he can endure a fast and physical style of play for the length of a game against strong and experienced top-level athletes.

“You have to play hard,” Bagley said, “and don’t complain.”

Bagley clearly has earned a level of respect competing each week in the Drew League. And it’s obvious that a player of his skills has surpassed any kind of high school basketball competition.

His best path to reaching the NBA as quickly as possible would be to meet whatever academic requirements are necessary to advance to college, put in his year there, then declare for the draft.

He seems to be following the words emblazoned on his warmup shirt: No excuse just produce.

eric.sondheimer@latimes.com

Twitter: latsondheimer