The San Diego Padres halted distribution of beach hats as a giveaway on Saturday after experts found what they believed to be grain beetles in some of the packaging containing the items.
The Padres said in a statement that they were advised that the grain beetles "pose no health risks to humans, but we decided to act out of an abundance of caution."
It was not immediately clear how the beetles were discovered. Fans who received the hats before Saturday night's game against the Colorado Rockies were asked to exchange them for vouchers.
Grain beetles are microscopic insects known to infest stored dry goods.
Ushers at Petco Park walked through the stadium and asked fans to drop their hats into plastic bags, according to The San Diego Union-Tribune, which also reported that the vendor who manufactured the hats will ship replacements to those with vouchers.