Russell was already committed to crossing the apex and running out to track limits at corner exit in Austin, when Sainz suddenly checked up and tried to cut inside of Verstappen. Russell shouldn't have overcommitted either, but the sudden move to the inside was a violation of iRacing 101-level racecraft -- you can always safely assume that some other dingbat is going to try and make a lunge into the first corner on race start, so if you're out front it's in your best interest to be as predictable as possible for the cars behind. As the old saw goes, you can't win a race in the first corner, but you sure can lose one -- and Sainz has lost two in the space of a year that way.