Professional Billiard Player

My client plays in a professional pool league and travels to tournaments
How do I claim her expenses?

Either your client has a hobby or a business

If your client is running a business and T2125 would be required.
Cash and the value of all winnings should de declared.
If taxpayer won a TV, cash value of the TV should be reported as income.

If this taxpayer spends more than he wins, CRA will most likely audit at some point and deem it to be hobby.

A business owner keeps detailed records of all wins ( dates, location) as well as entrance fees, travel expenses, etc…

Record keeping is key.

Thank you for your response
Very much appreciated

There’s a pretty celebrated case on a poker player (Duhamel) who got caught up in similar issues with CRA.

The light version is here (but you can read the case on CanLii too): Poker champion comes up a winner in high stakes showdown with CRA | Financial Post

Oddly, a counterpoint in Berube: Bérubé – Tax Court of Canada finds that, as shown by his winnings over a protracted period, a full-time poker player had a reasonable expectation of making a living at it | Tax Interpretations

Both provide something of a cautionary tale.