That first pedal downstroke when starting out is a very vulnerable position for the first couple of bikelengths. I learned that the hard way a few years back.
It was on one of my daughter's club rides, on a MUP that I've ridden dozens of times. We stopped for traffic at a road crossing.
Google Maps
The guy next to me started out, but decided mid-road he didn't have enough time to cross, and tried to panic stop. (Actually, there was plenty of time) In the process of stopping, he tipped his bike right in front of me. My foot was still on the downstroke and I didn't have good control when we collided in the middle of the road. Fortunately, nobody got hurt.
The lesson in that one for me is to always have 2 or 3 bike lengths clearance ahead when starting off. The lesson for the guy I hit was to stay the he** out of Amy's dad's way.
Edit: +1 on the driver in back being the one usually held responsible for a rear end crash