Wave overtopping of coastal structures is generally expressed in terms of average discharge and maximum overtopping volume. While substantial research can be found on the relationship of such variables with incident spectral characteristics and other geometrical dimensions, limited research has been done to identify the conditions for which severe individual overtopping events occur. The objective of the present work is to further investigate the statistical dependencies between individual overtopping volumes and incident wave characteristics and to identify the conditions which result in maximum overtopping events. To this aim, we statistically analyse timeseries of waves and overtopping events for the case of a vertical wall breakwater on a horizontal bed under non-breaking wave conditions. The timeseries are generated using a validated numerical model for 6 sets of boundary conditions. The analysis of the data shows that, among the examined variables, the incident wave crest level at the toe of the structure has the highest rank correlation with the individual overtopping volumes. Conversely, the incident wave heights show a lower rank correlation while the wave periods show no correlation at all. Additionally, by leveraging the tool of copulas we find that the incident wave crest levels have strong upper tail dependence with the individual overtopping volumes while the wave heights show no tail dependence. Subsequently, we examine possible dependencies with the wave group periods and wave group energy. We find that a moderate correlation exists between wave group periods and overtopping volumes but no upper tail dependence. Moreover, our results show that the fraction between the wave group energy and the group period has a high correlation and upper tail dependence with the overtopping volumes. Finally, we discuss possible practical applications of our findings as well as points for future research.