jag (n.1) Look up jag at Dictionary.com
"period of unrestrained activity," 1887, American English, perhaps via intermediate sense of "as much drink as a man can hold" (1670s), from earlier meaning "load of hay or wood" (1590s), of unknown origin. Used in U.S. colloquial speech from 1834 to mean "a quantity, a lot."
jag (n.2) Look up jag at Dictionary.com
"slash or rend in a garment," c.1400, of unknown origin.