Book 1, Page 179, Section 5.1.6.3 Brier score, the minimum of the Brier Skill Score

[StephenYin01]

The minimum of the Brier Skill Score $1 - \dfrac{BS}{BS_{\textrm{ref}}}$ should be $-\infty$ as $BS, BS_{\textrm{ref}} \in [0,1]$. Thus, if $BS_{\textrm{ref}} = 0$, then $BSS = -\infty$ for $BS \in (0,1]$.