  We discuss the physical meaning and the geometric interpretation of causality
implementation in classical field theories. Causality is normally implemented
through kinematical constraints on fields but we show that in a zero-distance
limit they also carry a dynamical information, which calls for a revision of
our standard concepts of interacting fields. The origin of infinities and other
inconsistencies in field theories is traced to fields defined with support on
the lightcone; a finite and consistent field theory requires a lightcone
generator as the field support.
