Complex sentence: In 1984, he became the first NHL on-ice official to wear a helmet; subsequently, several officials followed his lead and beginning with the 2006-07 NHL season, all NHL on-ice officials must wear helmets.
Split into simpler sentences: In 1984, he became the first NHL on-ice official to wear a helmet. Subsequently, several officials followed his lead and beginning with the 2006-07 NHL season, all NHL on-ice officials must wear helmets.