In the NHL there has been a huge number of changes since the sport first became popular, for example, the curvature of sticks was limited in rules introduced in the 1970s, as the previous designs with excessive curves provided less control and were ultimately more dangerous. This rule change resulted in improved shot accuracy but rather than causing an increase in goals, shots became more predictable for goaltenders.

Another major change from the earlier days of ice hockey was the improvements in goalie safety padding, with larger pads and chest protectors increasing the amount of space taken up the goalie. This led to a reduction in goals from around the late 1990s, so rule changes can often have a significant impact on the game and as a consequence, betting markets.