In his second stint as San Francisco 49ers defensive coordinator, Robert Saleh has shown his evolution as a defensive mind, bringing exotic blitzes and new coverage schemes to freshen up the defense.
His next evolution? A new base defense he brought out against the New Orleans Saints.
During the Week 2 game against the Saints, the Niners lined up safeties Jason Pinnock, Marquis Sigle, and J'Ayir Brown on the field together, along with their two cornerbacks and two linebackers. This defensive formation is known as a 4-2-5 defense, because there are four down linemen, two linebackers, and five defensive backs (with the three safeties).
A 4-2-5 defense is typically used when an offense has multiple tight ends or running backs on the field, but the defense still wants to guard against a pass. The hope is that the third safety keeps the physicality and run defense a normal base defense (like San Francisco's 4-3) would provide, but adds better pass coverage.
Given Brown's struggles in the preseason, which resulted in the 49ers' decision to turn to him in a 4-2-5 defense, is already surprising. However, the Niners have rarely considered using a 4-2-5 defense before, as their nickel corners and third linebackers have consistently been able to shoulder the load.
From Dre Greenlaw to Azeez Al-Shaiir, the 49ers have had third linebackers who can cover in space, and with K'Waun Williams and Deommodore Lenoir, they have had nickel corners who held their own in the run game. But these positions on the 2025 Niners are filled by rookies, with third-round pick Nick Martin an inactive linebacker and fifth-round pick Upton Stout struggling against the Seattle Seahawks in Week 1.
For both of these players, Saleh's decision to transition to a 4-2-5 may mean that they have yet to prove they can be trusted in all situations.
It'll be incumbent on them to prove that they can hold up to all situations and get on the field more consistently.