  We study basic properties of scalar hadronic resonances within a quantum
field theoretical toy model. In particular, we focus on the spectral function,
the mass and the decay width of the resonance $f_{0}(500)$. In this work, this
meson is understood as a seed state in an effective Lagrangian which couples to
pions. With such a setup we use the position of the pole on the second Riemann
sheet in order to obtain its spectral function. We confirm that $f_{0}(500)$
cannot be described by an ordinary Breit--Wigner function, and that a more
complicated structure is needed.
