Friesland has sporting traditions that deserve more than a novelty sidebar. Keatsen (Frisian handball), fierljeppen (competitive pole vaulting across water) and skûtsjesilen (racing traditional Frisian cargo sailing boats) remain organised sports/traditions with clubs, competitions and their own vocabulary.
Keatsen
Usually called kaatsen in Dutch and keatsen in Frisian, this ball game has a strong Frisian association structure. Look to the KNKB and local kaatsverenigingen for competitions, clubs and introductory opportunities.
Fierljeppen
Fierljeppen turns the traditional act of crossing waterways with a pole into a technical competitive sport. Do not attempt it independently on a random ditch: learn through an organised club/training location with proper equipment and instruction.
Skûtsjesilen
Skûtsjesilen is team sailing with historic skûtsjes. It is primarily something newcomers will encounter as a competition and regional cultural event rather than an activity you casually book like a rental boat. The SKS and IFKS organise prominent competition circuits.
Language matters
These traditions are closely connected to Frisian identity. You will see both Dutch and West Frisian terminology; preserving the Frisian names is part of understanding the culture rather than treating them as exotic curiosities.