Due to gyroscopic precession, changes to the rotor system are felt 90 degrees to the right or in the direction of the rotation.
A gyroscope provides rigidity in space, in that a spinning object does not want to change its position. The spinning rotor is a large gyroscope. When factors impact the rotor disc, the pilot will experience the effect 90 degrees to the right or in the direction of rotation. Below are the two primary examples:
Retreating Blade Stall: With retreating blade stall, the blade angle is at its greatest when the blade is directly to the left or 270 degrees. However, the effect is felt over the tail, as the tail drops, which pitches the nose of the helicopter up.
Transverse Flow (Inflow Roll): Transverse flow causes less lift at the rear of the rotor disc, but the helicopter will roll to the right as the effect is felt 90 degrees to the right.
The helicopter designers take gyroscopic precession into account, so the pilot does not need to worry about it during flight.
FAA-H-8083-21A – Helicopter Flying Handbook pg. 2-16
Principles of Helicopter Flight, 2nd Edition, pg. 177
FM 3-04.203-2007 Fundamentals of Flight pg. 1-17