An intuitive understanding of the phenomenon comes from Newton's third law, that the deflective force on the body is a reaction to the deflection that the body imposes on the air-flow. The body "pushes" the air in one direction, and the air pushes the body in the other direction. In particular, a lifting force is accompanied by a downward deflection of the air-flow. It is an angular deflection in the fluid flow, aft of the body.
Lyman Briggs made a wind tunnel study of the Magnus effect on baseballs, and others have produced images of the effect. The studies show that a turbulent wake behind the spinning ball causes aerodynamic drag, plus there is a noticeable angular deflection in the wake, and this deflection is in the direction of spin.
The process by which a turbulent wake develops aft of a body in an airflow is complex, but well-studied in aerodynamics. The thin boundary layer detaches itself ("flow separation") from the body at some point, and this is where the wake begins to develop. The boundary layer itself may be turbulent or not, and that has a significant effect on the wake formation. Quite small variations in the surface conditions of the body can influence the onset of wake formation and thereby have a marked effect on the downstream flow pattern. The influence of the body's rotation is of this kind.
It is said that Magnus himself wrongly postulated a theoretical effect with laminar flow due to skin friction and viscosity as the cause of the Magnus effect. Such effects are physically possible but slight in comparison to what is produced in the Magnus effect proper. In some circumstances the causes of the Magnus effect can produce a deflection opposite to that of the Magnus effect.
The diagram above shows lift being produced on a back-spinning ball. The wake and trailing air-flow have been deflected downwards. The boundary layer motion is more violent at the underside of the ball where the spinning movement of the balls surface is forward and reinforces the effect of the balls translational movement. The boundary layer generates wake turbulence after a short interval.
In baseball, this effect is used to generate the downward motion of a curveball, in which the baseball is rotating forward (with topspin). Participants in other sports played with a ball also take advantage of this effect.
On a cylinder, the force due to rotation is known as Kutta–Joukowski lift. It can be analysed in terms of the vortex produced by rotation. The lift on the cylinder per unit length, , is the product of the freestream velocity,  (in m/s), the freestream density of the fluid, (in kg/m), and circulation of fluid established by the rotation, , due to viscous effects:
where the vortex strength (assuming that the surrounding fluid obeys the no-slip condition) is given by
where ω is the angular velocity of the cylinder (in rad/s) and r is the radius of the cylinder (in m).