NHL clubs tightened Covid-19 protocol on Thursday with four teams having halted their season over positive tests, the latest belonging to Buffalo Sabres coach Ralph Krueger. The new measures announced by NHL officials include the removal of glass behind team benches in arenas to create a better air flow, with clubs asked to install portable air cleaners behind club seating areas. The league also mandated that players and team staff cannot arrive at arenas more than one hour and 45 minutes before the start of games except in cases of injury treatment. When they arrive in locker rooms, players must have at least six feet between their space and other players. All team meetings on gamedays and off days will be conducted virtually. The move comes after nearly two dozen games have been postponed since the NHL season began January 13 with nearly 90 players having been put onto the Covid-19 absentee list since the campaign launched. The New Jersey Devils, Minnesota Wild, Buffalo Sabres and Vegas Golden Knights seasons are on hold, with Vegas set to return to the ice Friday. In all, there are 40 NHL players currently on the Covid-19 list. New Jersey has 17 players on the list and won't resume before Tuesday. Buffalo is off until next Thursday at home against Washington with four players on the list and Krueger, 61, isolating after returning a positive result Thursday. js/rcw