The harried spawner darts left and right, finning back and forth, never able to guard all corners as vicious little bream nip and tuck from the rimming weeds. The vulnerable bass cannot drive away all attacks, but what she can do is knock the hell out of the occasional careless bluegill that lingers too long. The bass is in a defensive mode, trying to slam the offender and remove it from the bed. A lure with a bluegill pattern can play to this advantage. Both threadfin shad and bluegill sunfish represent prime forage for bass, but the bream has become a mortal enemy during the buds of spring.
Any lure perceived as a real threat to the nest has the trump of drawing a defensive strike.
The ethics of deliberately casting to a bass protecting a nest are a matter of ongoing debate, and my intention is not to promote unsportsmanlike tactics. Whether the disruption was accidental or deliberate makes no difference. It's your call. All I'm saying is that a bluegill sunfish, more so than a threadfin shad, can light a fire in the weedbeds when bass move to spawn. But it's not over.