I like to grid the entire area first and remove all signals (good & bad), then go back after some time and look for fresh drops. I like to hunt the chair lines along the sidelines - that's the most likely area for people to drop things, then the goal areas. Been a good pattern for years now - the same fields keep producing gold on follow-up visits. This particular soccer field produced a 14K chain (18" long), a 16K coin pendant (laser cut/unicorn - country unknown), a 14K bracelet (Italy), and a 22K ring (rose gold - with flowers / Middle Eastern). Those 4 gold items were recovered in an hour and a half during the first return visit after grooming (about 6 months prior). The 18K cat charm was recovered in 30 minutes 3 months after that.
Give it a try sometime - I do the same pattern with small swimming area beaches, football fields, grassy parks, and kids playgrounds.
Good luck to you!
Richard
San Diego