A 23-year-old man suffered life-threatening injuries after being stabbed in the chest during a fight early Saturday morning in Allston, Boston police said. Officers were called to the Tavern in the Square on Brighton Avenue at about 2:20 a.m. and found the victim across the street. He was taken to Beth Israel Deaconess Medical Center, said Officer Nicole Grant, a police spokeswoman. No arrest has been made, and no weapon was found. An investigation is ongoing.