Quarter (qtr or Q) [8] : A unit of relative time used in sports, equal to 1/4 the total playing time of a competition. A quarter is 15 minutes in American football, 12 minutes in professional basketball
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}