All Israel heard say that Saul had struck the garrison of the Philistines, and also that Israel was had in abomination with the Philistines. The people were gathered together after Saul to Gilgal.
So Jonathan was out wiping out the Philistines and Saul was around blowing the trumpet, and taking the glory and announcing that he had smitten the Philistines so that the Israelites heard that Saul had smitten the Philistines with a great slaughter.