CLEVELAND -- As the explosion echoed through Jacobs Field, players stopped in their tracks, a few ducked for cover and Philadelphia manager Larry Bowa cringed.

"I didn't know what is was,'' Bowa said. "These days you think the worst.''

The explosive device was thrown from the upper deck during the Indians' game against the Phillies on Tuesday night, burning two people -- one an Indians employee.

"It looks like either it was homemade or something that is restricted to a pyrotechnics professional,'' Cleveland Fire Chief Kevin Gerrity said.

The three men suspected of throwing it -- Donald Kreiger, 22; Clifton Oliver, 22; and Andrew Mendez, 20, all of Elyria -- remained in jail Wednesday night. They had not been charged but were being held on suspicion of felonious assault and aggravated arson.

Fire Lt. Clayton Cunningham said investigators want to be sure what was set off before deciding what to do about charges.

Witnesses said the device was about 8 inches long. It shattered the plastic name tag on usher Brian Burke's chest and burned Judith Knight's legs, police said.

Knight, 43, of Strongsville, was leaving the game when the device exploded a few inches from her. She was treated at MetroHealth Medical Center and released.

"She was pretty shaken up,'' Indians spokesman Bob DiBiasio said.

Burke's chest was burned. He was treated at Jacobs Field.

The blast in a lower-level smoking area was heard throughout the ballpark in the top of the ninth inning of the Indians' 5-1 victory.

"I looked around for smoke,'' Indians designated hitter Ellis Burks said. "And all the fans got really quiet.''

Burks said he doesn't feel unsafe on the field, but worries about how fans could be susceptible in today's uncertain times.

"With the stuff that's going on, you come out to a ballgame and you are open prey for a terrorist or anybody,'' Burks said. "All it takes is for somebody to do something stupid.''

A few of the players on the field ducked their heads, and both dugouts emptied when the explosion went off at 9:23 p.m.

"It was loud,'' Indians manager Charlie Manuel said. "It sounded like two trucks running together.''