Consider this quote:
DROP OF A HAT - Acting readily or on some single signal. In the 19th century it was occasionally the practice in the United States to signal the start of a fight or a race by dropping a hat or sweeping it downward while holding it in the hand. The quick response to the signal found its way into the language for any action that begins quickly without much need for prompting.
Looking up OALD, there are three definitions that seems relevant to the context, but I'm not sure which one is the most appropriate, they are:
1 [uncountable] action rather than ideas
the theory and practice of teaching
She's determined to put her new ideas into practice.
2 [uncountable, countable] a way of doing something that is the usual or expected way in a particular organization or situation
guidelines for good practice
a review of pay and working practices
child care policy and practice
3 [countable] a thing that is done regularly; a habit or a custom
the German practice of giving workers a say in how their company is run
It is his practice to read several books a week.