Red Sox pitcher Joe Kelly even sported a referee outfit ahead of the team's trip to Minneapolis, where they will play a three game series against the Minnesota Twins. That series begins at 8:10 p.m. Tuesday at Target Field.
Brock Holt wore an Iceland jersey. Sandy Leon -- a Venezuela native -- wore a Colombia jersey.
"Go Iceland ... woo," Holt said in a Twitter video posted by the Red Sox.
Kelly also held a penalty flag and blew a whistle as the Red Sox were boarding team busses. Several other players joined the pitcher in wearing the referee gear.
"With the umpires of the game today," Red Sox pitcher and Mexico native Hector Velazquez tweeted, along with a photo of the team's 'referees.'
The Red Sox (49-24) beat the Mariners 9-3 on Sunday at Safeco Field and split the four-game series in Seattle.
Iceland tied Argentina 1-1 in their Group D opener on Saturday and battles Nigeria at 11 a.m. on Friday in Russia.
Colombia battles Japan in Group H at 8 a.m. Tuesday. Brazil tied Switzerland 1-1 on Sunday and faces Costa Rica on Friday.