In the US the season for football is split into the 4 seasons. The busiest time is across the summer, for the camps which is why the demand for summer coaches is higher than the rest of the year. 9 Month contracts run from March to November to cover team coaching that companies often have, which involves being a trainer to different teams just doing the sessions on different nights.
September on wards is often when you have rec sessions and travel teams start again. Winter is mainly seen as the close season, with not as much soccer being played. That's why the main contracts finish is Nov then don't start again until March.
Although this will all depend on the state you are, and the set up of the company or organisation. I was in New Jersey for 5 and a half months.