In order to come up with a good, playable, scenario, first let me know how many people you have to work with?
My initial thoughts, based on what you are asking for, would be modeled on the takedown of Pablo Escobar in Columbia. You would have 1)Escobar and his Medellin bodygaurds, 2)the "Search Bloc" unit of the Columbian police, and 3)a small group of CIA contractors. Rules would require the "CIA contractors" to stay back at a certain distance and not engage in CQB (think snipers).
In terms of setup, it would be an assault on the already in place Medellin by the Search Bloc, with sniper covering fire from the Contractors. Win conditions for the Contractors/Search Bloc is to kill "Pablo", win conditions for the Medellin would be to get Pablo away "safe", maybe to one of several field exits points.