  We consider head-on collisions of two particles near the event horizon.
Particle 1 is outgoing, particle 2 is ingoing. We elucidate, in which case the
energy $E_{c.m.}$ in the center of mass frame can grow unbounded. If the proper
time between the horizon and an arbitrary point outside it for particle 1 is
finite, we deal with a white hole. If it is infinite, we deal with a black
hole. Particles can be either free or experience the action of a finite force.
Our results are complementary to those for the standard BSW effect when
particles move in the same direction. The results rely on classification of
particles developed in our previous work H.V. Ovcharenko, O.B. Zaslavskii,
Phys. Rev. D 108, 064029 (2023).
