inorganic chemistry - Why chlorine acts as a strong field ligand in tetrachloridoplatinate(II)?

In most of the cases I have learnted, halogens act as a weak field ligand. However, I recently learned somewhere on the web that the strength of a ligand also depends upon the size of the atom. A classic example is tetrachloridoplatinate(II): $\ce{[Pt(Cl)4]^2-}$.

Why is it so, and how can I predict the hybridization correctly in such exceptions, if I come across them for the first time?