At Arsenal United fan starts to dance so wildly it makes ground shake (15)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

*(AT ARSENAL + U (=United, as in Man U ) + FAN + D <ance> S <o> (“starts to” means first letters only)); “wildly” is anagram indicator; cryptically, one can say that, as a cause of earthquakes, the San Andreas Fault “makes (the) ground shake”!