Fully nonlinear numerical simulations performed with the HOS method reveal that Peregrine breather solution has a high probability to persist even in a chaotic environment and that the maximum amplification factor of such breather dynamics can be larger than the theoretical prediction in the regular background wave. The maximum wave height attainable and the corresponding spatial evolutionary distance required are significantly affected by the initial background waves. The formation of abnormal wave induced by breather dynamics is mainly a localized behaviour, strongly dependent on the initial wave energy and detailed structure of the wave group. The influence of initial condition uncertainty on the profile of maximum wave, defined by both zero-up-crossing and zero-down-crossing methods, is investigated in the numerical tank constructed with CS model based on the Monte Carlo simulation approach. To describe the variation of the profile of maximum wave, six parameters are proposed and estimated with statistical method. The extreme heights in a sea state are only sensitive to the amplitudes of a certain range of free waves and three types of uncertainties can be identified in the initial conditions involving the natural, knowledge and mixed uncertainties, contributing a lot to the versatility of the profile of maximum wave.