It's the individual entity, company, business etc. that is VAT registered. Then, depending on the activity that may attract VAT at either 0 , 13.5 or 21%. I have not often encountered GAA teams being VAT registered, although certain clubhouse activities, e.g. a licensed bar, might be. Unless they provide a VAT invoice with a VAT number etc. you cannot assume VAT is included.
If they are VAT registered and if the activity now proposed is VATable then they should issue the appropriate invoice at whichever rate is applicable.
If they are not VAT registered then there will be no VAT charged.
Either way you do not have to "worry" about the VAT as it is up to the person being paid to ensure that VAT is charged where applicable. If you are charged VAT then, subject to it being a business related supply, then you will be entitled to a VAT input credit at whichever rate.
non commercial sporting activities by a not-for-profit organisation can be vat exempt, so it's possible that VAT may not apply, but the only way you will know is to ask the entity concerned if they will be charging VAT or not.