  Feedback effects due to spin fluctuation induced precursors in the fermionic
quasiparticle spectrum are taken into account in the description of a quantum
critical point of itinerant spin systems. A correlation length dependent spin
damping occurs, leading to a dynamical scaling with z\approx 1 which
non-trivially competes with the conventional spin wave behavior. We obtain,
within a one loop renormalization group approach, a quantitative explanation
for the scaling behavior seen in underdoped cuprate superconductors.
