Stallworth was headed toward the beach when he hit Mario Reyes, 59, around 7 a.m., said Miami Beach police spokesman Juan Sanchez. The unidentified pedestrian was taken to a nearby trauma center, where he was pronounced dead about an hour later. Reyes was near a crosswalk but it's not clear if he was crossing legally.
Stallworth, 28, was cooperating and no charges have been filed, Sanchez said. Officers drew blood to test for drugs or alcohol, which is routine. Sanchez said results from the blood test could take anywhere from three days to three weeks.
Police would not say where Stallworth was coming from or where he was headed, and Sanchez didn't have anymore information about Reyes.
Miami-Dade County property records show Stallworth owns two condos in a building on Biscayne Boulevard in Miami not far from the causeway and another condo in a different building in Miami.
A message seeking comment was left on the voicemail of his agent, Drew Rosenhaus.
The Browns said in a statement they were aware of what happened.
"We understand the seriousness of this situation, but will not have any further comment at this time as this is an ongoing investigation," the team said.
Stallworth signed a seven-year, $35 million contract with the Browns as a free agent before last season but hardly played because he was hurt. He was due a $4.75 million signing bonus Friday.
Stallworth, who previously played for New England, Philadelphia and New Orleans, finished last season with just 17 catches for 170 yards. He was slowed all season by a nagging hamstring injury and made just seven starts for the Browns.
Stallworth had his best season with the Saints in 2005, when he made a career-high 70 receptions for 945 yards and seven touchdowns. He was drafted in the first round (No. 13 overall) by the Saints in 2002. Stallworth played his college ball at Tennessee.