A sidesplat is a shot/effect in a film in which a character, usually while walking across a street in a somewhat distracted state of mind is suddently slammed by a fast moving vehicule that explodes into the frame from offscreen left or right.
The shot often begins quietly , sometimes in slow motion, before a sudden burst of sound of the motor screaming, tires screeching, and/or horn of the vehicule. This of course adds to the jolting effect of the regular speed visual of the crash.
There are several examples of this effect from different movies.

When you eat dirt for the first time and leave your family to build a shack in the woods