An influence block is a quick, deceptive blocking action that attempts to confuse defenders coached to react to the offense's blocking techniques.
The blocker gives the defender a familiar cue through movement or contact, triggering a response. That response can make the defender easier for someone else to block or move him away from the run.
Coaches can teach the influence block as an add-on to a play's blocking scheme. The blocker needs to know what response his action will likely draw; his teammates need assignments that take advantage of the defender's reaction. An offense can install an influence block as a tag to call when an aggressive defender is reading his block correctly and is talented enough to beat it with proper technique. By modifying that block, the offense makes the defender expect a different play. He reacts to the apparent block and puts himself in the wrong position.
When teaching an influence block, it helps if your offense already understands the blocks they execute on complementary plays. Players who have repped related plays can recognize the movement or contact that prompts a defensive reaction. They can then use the influence block to draw that reaction when it puts the defender out of position.
A successful influence block is intended to make the defender hesitate on later plays: the same cue may now mean the expected block or another setup.