[Rich Ives]

Collisions are NOT illegal. Certain aspects MAY make it illegal but not automatically.

From the NCAA rule book.. Look especially at the underscored parts. Bottom line is that from your description the blame, if there is any to be assigned, belongs on the catcher.

Collision Rule

SECTION 7. The rules committee is concerned about unnecessary and violent
collisions with the catcher at home plate, and with infielders at all bases. The
intent of this rule is to encourage base runners and defensive players to avoid
such collisions whenever possible.

When there is a collision between a runner and a fielder who clearly is in
possession of the ball, the umpire shall judge:

If the defensive player blocks the base (plate) or base line with clear possession
of the ball, the runner may make contact, slide into or make contact with a
fielder as long as the runner is making a legitimate attempt to reach the base
(plate). Contact above the waist that was initiated by the base runner shall not
be judged as an attempt to reach the base or plate.

1) The runner must make an actual attempt to reach the base (plate).
PENALTY—If the runner attempts to dislodge the ball or initiates an
avoidable collision, the runner shall be declared out, even if the
fielder loses possession of the ball. The ball is dead and all other
base runners shall return to the last base touched at the time of
the collision.

2) The runner may not attempt to dislodge the ball from the fielder.
Contact above the waist shall be judged by the umpire as an attempt by
the runner to dislodge the ball.
PENALTY—If the contact is flagrant or malicious before the runner touches
the plate, the runner shall be declared out and also ejected from
the contest. The ball is immediately dead and all other base
runners shall return to the last base touched at the time of the
collision.

3) The runner must attempt to avoid a collision if he can reach the base
without colliding.
PENALTY—If the contact is flagrant or malicious after the runner touches the
base (plate), the runner is safe, but is ejected from the contest.
The ball is immediately dead and all other base runners shall
return to the last base touched at the time of the interference. If
this occurs at any base other than home, the offending team may
replace the runner. If the contact occurs after a preceding runner touches home
plate, the preceding runner is safe. The ball is immediately dead
and all other base runners shall return to the last base touched
at the time of the contact.

4) If the runner’s path to the base is blocked and (1), (2) and (3) are fulfilled,
it is considered unavoidable contact (see Rule 2-54, Obstruction).