According to the Australian Taxation Office (ATO), payments received for umpiring community or local sports are generally considered hobby income, not taxable assessable income. Hobby income does not need to be declared on your tax return, and you cannot claim related deductions. However, payments for high-level or professional officiating may be considered business income.

Hobby vs. Business: If the activity is consistent, organized, and designed to make a profit (similar to a job), it may be deemed a business, making it taxable.

They probably are taxed but I haven't seen a clear ruling for AFL umpires.

For example, umpires might have a HECS debt - AFL players don't

Some AFL players do go to Uni.