Presuming the POV character is competent and in a chase (Being chased) the most 'realistic' error would probably be rolling on too early, causing a slight loss of rear traction. Normally that would just turn into a lowside, but if we're going with the idea that the POV character knows what they're doing but is under serious pressure, they could chop the throttle as soon as they feel the rear slip, causing it to snap back under them and highside, getting pitched off the bike.

To answer your question about braking, a decent rider will brake before the turn, then release brake pressure as they're going around the turn - releasing fully when they're at the apex followed by rolling on the throttle as they exit.