  We study initially unbound systems of two black holes using numerical
relativity (NR) simulations performed with GR-Athena++. We focus on regions of
the parameter space close to the transition from scatterings to dynamical
captures, considering equal mass and spin-aligned configurations, as well as
unequal mass and nonspinning ones. The numerical results are then used to
validate the effective-one-body (EOB) model TEOBResumS-Dal\'i for dynamical
captures and scatterings. We find good agreement for the waveform
phenomenologies, scattering angles, mismatches, and energetics in the low
energy regime ($E_0\lesssim 1.02\,M$). In particular, mismatches are typically
below or around the $1\%$ level, with only a few cases -- corresponding to
spinning binaries -- slightly above the $3\%$ threshold. We also discuss
dynamical captures in the test-mass limit by solving numerically the Zerilli
equation with the time domain code RWZHyp. The latter analysis provides
valuable insights into both the analytical noncircular corrections of the EOB
waveform and the integration of NR Weyl scalars.
