  A type of bag function is proposed to make the MIT bag surface of baryon
dynamical. It is illustrated through renormalization of the quark field that
the softening of chiral bag gives rise to a model of chiral quark with
effectively-generated mass of quark, in which confined quark moves in the
background of nonlinear pion. A prediction of bag constant $B$ $\simeq
2f_{\pi}^{2}m_{\pi}^{2}\allowbreak $ is made. With two free parameters, the
self-coupling $e$ of pion and the confining scale $a$, the computed mass, the
charge root-mean-square radius and magnetic moment of the proton are in good
agreement with the experimental values.
