John Gill Commentary Acts 19:40

"For indeed we are in danger to be accused concerning this day`s riot, there being no cause [for it]: and as touching it we shall not be able to give account of this concourse." — Acts 19:40 (ASV)

For we are in danger of being called in question
Or are liable to be called to an account, reproved, and punished by the Roman proconsul, appointed over this city, or by the Roman emperor, or the Roman senate: for this day's uproar; it being capable of being interpreted as a riot, tumult, and sedition:

there being no cause by which we may give an account of this
concourse :
or no reason can be assigned, why such a number of people should gather together; none can be given that will justify it, or that can be alleged in favour of it.