Ok grid. For the ops group you can also start with 'st' to make stops, store, stamp, and start. And for the hampton group you've included the 'h' in north but not in the other 3 which confuses things a little. You'd add 'ampton' to that word but 'hampton' to the other three.

Unfortunately one of your groups has two possible answers and one isn't coded as acceptable

Good fun - just so you know, I got champ, chart etc wrong as these words can also all be preceded by ST.