Dig. 9.2.11 in principio

 Mela writes that if some persons were playing ball and one of them hit a ball quite hard and hit a barber's hands who was shaving a slave and the razor cut the slave, the lex Aquilia would lie with the person who was culpable.

Proculus wrote that the culpa lies with the barber.

Ulpianus 18 ad ed.

Item Mela scribit, si, cum pila quidam luderent, vehementius quis pila percussa in tonsoris manus eam deiecerit et sic servi, quem tonsor habebat, gula sit praecisa adiecto cultello: in quocumque eorum culpa sit, eum lege aquilia teneri.   Proculus in tonsore esse culpam: et sane si ibi tondebat, ubi ex consuetudine ludebatur vel ubi transitus frequens erat, est quod ei imputetur: quamvis nec illud male dicatur, si in loco periculoso sellam habenti tonsori se quis commiserit, ipsum de se queri debere.