While most "grinders" will fight, some do not; "grinder" refers specifically to a style of defensive hockey which is within the rules of the game. Sometimes grinder is used in combination with "mucker" to describe a player as a "mucker and a grinder", although it is used as emphasis. In this context, mucker is largely synonymous with grinder.
In hockey, a "grinder" refers to an individual who plays a defensive style within the game's regulations. Some players may not exhibit this behavior, but when they do, it's often accompanied by the term "mucker", which conveys a similar meaning.