  A new pyrochlore compound, NaCaNi$_2$F$_7$, was recently synthesized and has
a single magnetic site with spin-1 Ni$^{2+}$. We present zero field (ZF) and
longitudinal field (LF) muon spin rotation ($\mu$SR) measurements on this
pyrochlore. Density functional theory (DFT) calculations show that the most
likely muon site is located between two fluorine ions, but off-centre. A
characteristic F-$\mu$-F muon spin polarization function is observed at high
temperatures where Ni spin fluctuations are sufficiently rapid. The Ni$^{2+}$
spins undergo spin freezing into a disordered ground state below 4~K, with a
characteristic internal field strength of 140~G. Persistent Ni spin dynamics
are present to our lowest temperatures (75~mK), a feature characteristic of
many geometrically frustrated magnetic systems.
