  Understanding the role of lattice geometry in shaping topological states and
their properties is of fundamental importance to condensed matter and device
physics. Here we demonstrate how an anisotropic crystal lattice drives a
topological hybrid nodal line in transition metal tetraphosphides $Tm$P$_4$
($Tm$ = Transition metal). $Tm$P$_4$ constitutes a unique class of black
phosphorus materials formed by intercalating transition metal ions between the
phosphorus layers without destroying the characteristic anisotropic band
structure of the black phosphorous. Based on the first-principles calculations
and $k \cdot p$ theory, we show that $Tm$P$_4$ harbor a single hybrid nodal
line formed between oppositely-oriented anisotropic $Tm~d$ and P states
unhinged from the high-symmetry planes. The nodal line consists of both type-I
and type-II nodal band crossings whose nature and location are determined by
the effective-mass anisotropies of the intersecting bands. We further discuss a
possible topological phase transition to exemplify the formation of the hybrid
nodal line state in $Tm$P$_4$. Our results offer a comprehensive study for
understanding the interplay between structural motifs-driven mass anisotropies
and topology in anisotropic lattice materials to realize hybrid semimetal
states.
