From CAL's Website:

A long awaited season start is now a reality. Caleague is happy to announce the start of the 1st Left 4 Dead Season Sunday, Feb. 1st. All teams make sure you are up-to-date on the rules, our updated match mod, server configs, and CAL ACS(anti-cheat). All can be located in our file section located in the Left 4 Dead section on the CAL site.