An OT cutting off a 4i is difficult which was illustrated in the prior post.
The ILB is able to stack and fall back protected from the OT by the 4i.
Many offensive coaches have borrowed a solution from veer option teams, arc block the OT to the ILB.
The theory is simple. The 4i is the read key, the OT will outside (arc) release the 4i allowing a free climb to the ILB.
The assumption is the defense is playing scrape exchange which should result in easy blocks.
The offense is assuming the 4i will chase the dive, causing a keep from the QB. The ILB should be getting a face full of OT creating a tough run fit for the defense.
The reality is many 4i's and LB's are reading the blocking scheme. Against the cutoff block as in the first diagram the 4i will look to beat the cutoff and chase the dive. The result is the scrape exchange with the ILB. However against the OT on an arc block the 4i many not chase the dive.
The 4i is keying the OT. When the OT arcs the 4i can widen. For the QB the read key widens which should trigger a give read. The 4i widens playing square to controlling for the QB and cutback. The ILB sees the B gap widen as the 4i widens, triggering a fill read. The arc block of the OT is wasted when the ILB doesn't scrape outside and instead fills.
Here is a good example from LSU