What does Boxing Day have to do with boxing?
1530s, "contraction of a word by omission of middle sounds," from Medieval Latin syncopationem (nominative syncopatio) "a shortening or contraction," from syncopare "to shorten," also "to faint away, to swoon," from Late Latin syncope (see syncope). Musical sense is attested from 1590s.
in music, the displacement of regular accents associated with given metrical patterns, resulting in a disruption of the listener's expectations and the arousal of a desire for the reestablishment of metric normality; hence the characteristic "forward drive" of highly syncopated music. Syncopation may be effected by accenting normally weak beats in a measure, by resting on a normal accented beat, or by tying over a note to the next measure