Simply put, Cover 3 divides the field into 3 vertical sections. Cover 4 divides the field into 4 vertical sections.
Cover 3 has 1 deep safety and the other safety plays closer to the LOS. He helps cover TEs, RBs, and the flat as well as being a force against the run. Cover 4 plays both safeties deep. They provide deep help on the deeper passing game and are not as effective on the underneath routes and defending the run.
I mentioned Cover 3 because Trubisky has not challenged teams down the field and has thrown a lot of shorter passes.
Does that help? I'll answer more questions if you have them.
That's helpful to me.
Is it safe to say Cover 3 has tighter coverage or will the tightness of coverage vary depending on how the defense decides to play it?
I don't know about "tighter," but Cover 3 has more man tendencies than Cover 2 or 4. It's still very much a zone defense, but the corners can trail the WRs all the way up the sidelines. Cover 2 and 4 are safer. Cover 3 is a bit more aggressive. For example, Baltimore was in Cover 3 last week against Miami and were burned repeatedly deep by very fast WRs in T. Hill and Waddle. Cover 3 can be exploited by deep passing attacks. Cover 2 and 4 are safer, but not as aggressive in coverage.
