In terms of the Points Race, there does not appear to be a rule in the UCI Cycling Regulations Part 3: Track Races, under the Points Race section, that specifically talks about a collisions between riders. The closest ruling is in the event of a recognised mishap.
In the case of a recognised mishap, the rider shall be entitled to a neutralisation during the number of laps closest to 1300 metres. On returning to the track, he shall resume the position he occupied before the mishap.
Earlier in the same document (page 7), it describes what a "recognised mishap" is:
3.2.021: Recognised mishap
The following shall be considered recognised mishaps:
- a fall
- a puncture
- the breakage of an essential part of the bicycle.
All others incidents are considered un-recognised mishaps.
Now, whether a fall covers rider collisions is up for debate.
However, on page 6 under the Warnings - disqualification section:
3.2.013: Warnings - disqualification
Any offence not specifically penalised and any unsporting behaviour shall be punished by a warning, indicated by a yellow flag, or by disqualification from the race, indicated by a red flag, according to the gravity of the fault, notwithstanding the
fine provided for in article 12.1.007.
So we can reasonably assume that Mark Cavendish was adjudged to have caused the crash, but it was not considered to be that serious of an offense to be disqualified, and was given a warning.
In terms of other track cycling events, it will again come down to that specific event to explicitly define rules for crashes, otherwise it will follow the guidelines in section 3.2.013 (above).
An example of an event which does have specific rules regarding crashes is the Sprint event. It says:
Before the last 200 metres line or the start of the final sprint, riders may avail themselves of the full width of the track but must nevertheless leave sufficient space for their opponent to pass and shall refrain from any manoeuvres that could provoke a collision, a fall or cause any rider to ride off the track.
3.2.048: Race Stoppages
The race may be stopped only:
- in the case of fall.
If the fall be intentionally caused by a competitor, that competitor shall be
relegated or disqualified from the tournament according to the gravity of the
fault committed and the other competitor declared the winner. In three or fourup
heats, the race shall be immediately restarted with the remaining two or
Should the fall have been caused by a competitor riding too slowly in a curve
or by any other unintentional fault, the race shall be restarted and the
offending rider shall take the inside of the track.
If the fall is not caused by a competitor committing a fault, commissaires shall
decide whether the race is to be restarted with the riders in the same order or
whether the positions at the time of the fall should be considered final.