Halman was at home in Rotterdam, Holland, where police found him bleeding from a knife wound, but officers were unable to resuscitate the outfielder.
Under Dutch privacy rules officials were unable to give his name, but they said: "A 24-year-old died this morning in a stabbing and we have arrested the 22-year-old brother of the victim."
Dutch TV station NOS confirmed the news however, after speaking with his family.
There's no info on what sparked the deadly brawl between the pair.
Hallman's father was a pro in Holland and his brother reportedly play in the World Baseball Championship, but it was the 24-year-old Mariner who was the most successful battting a .230 with two homers and six RBIs in 35 games with the Mariners last season.