Both. Stroll knew Verstappen was close, he should have left some room (especially knowing it was Max.) However, Verstappen didn’t have to dive in the corner like that. I blame both because this was free practice, not the race and there was no reason to fight for a corner like that. Just back off and wait for another turn. Of course, Verstappen went into some stupid little rant on the radio. He’s incredibly talented, but he’s also an entitled, arrogant brat who thinks he owns F1.
To me, that incident is typical of the current generation of drivers who don’t seem to know basic racing etiquette. They think that today’s cars are so safe that they can’t get hurt, so they slam into each others without thinking of the consequences. You didn’t see crap like that back in the days of Lauda, Andretti or Clark. These were real racers who didn’t learn their trade on simulators. They understood that they could get killed if they crashed. I have a lot more respect for these men than for a petulant child like Verstappen.