Haas' running in first practice for the Monaco Grand Prix was halted in bizarre fashion after Romain Grosjean and Kevin Magnussen were black-flagged. Both drivers' radio systems failed during FP1, rendering Haas unable to communicate with their drivers.
Black flags are rarely seen in F1 sessions, generally reserved for moments of dangerous driving.
However, Magnussen and Grosjean were far from safe as the team could not inform them of traffic, or when to return to the pits.
Haas said in a brief statement that their pit boards "weren't doing the business" so the FIA stepped in and stopped both drivers from running.