I have all toddlers in my care so every day there is a thrower at lunchtime.
I will give a glare with a "No throwing!" then if it happens again their tray is removed and they can sit there in their chair until mealtime is over. My highchairs have them firmly buckled in so they can't climb out. I also make a point of having the food thrower be the LAST one that gets down. Usually does the trick.