  The variables appropriate for the infrared limit of unconstrained SU(2)
Yang-Mills field theory are obtained in the Hamiltonian formalism. It is shown
how in the infrared limit an effective nonlinear sigma model type Lagrangian
can be derived which out of the six physical fields involves only one of three
scalar fields and two rotational fields summarized in a unit vector. Its
possible relation to the effective Lagrangian proposed recently by Faddeev and
Niemi is discussed.
