The incident followed Double-A Frisco's controversial 6-5 loss to the Missions. RoughRiders designated hitter Mike Bianucci slugged an apparent go-ahead three-run homer in the top of the ninth inning, but the play was ruled a double that left Frisco behind by a run.
Manager Steve Buechele and pitching coach Jeff Andrews were ejected for arguing the call, and an altercation broke out afterward involving fans and members of the RoughRiders. Beltre allegedly tossed a trash can and bats into the crowd.
"I was standing there and all of a sudden, a trash can came flying out of the dugout," Missions president Burl Yarbrough told the San Antonio Express-News. "I've been here 24 years and I've never seen anything like this."
At least two fans reportedly were arrested, but attempts to reach San Antonio police were unsuccessful.
"That was kind of scary," Missions DH Cody Decker told the newspaper. "It's something you never want to see at a baseball game."
According to MLB.com, Beltre will be assigned to extended spring training in Arizona while he serves the suspension, which will last 15 games.
"We are going to continue to look at it as far as the involvement of other people," Rangers general manager Jon Daniels said. "It's not something we're going to condone. It's something we take seriously. It was a black eye for all involved. We do not know everything that happened, but we're looking into it."
Beltre, 21, is one of the Rangers' most highly touted prospects. Acquired from the Red Sox in the 2007 trade involving Eric Gagne, he's hitting .253 with five RBIs and three stolen bases in 18 games.
The native of the Dominican Republic started last season at Bakersfield and tore up the Class A Advanced California League with a .331 average, five homers, 35 RBIs and 10 steals in 68 games. The Rangers promoted him to Frisco, where he hit .254 with a homer, 14 RBIs and eight stolen bases in 47 games.