The process involves getting hold of a copy of your UK police record (even if it's completely blank). That can take up to 40 days. (Fee �10). [It's also possible that they might demand a copy of your Spanish criminal record]. You then have to make an appointment to attend the US embassy in London for an interview. (Application fee $100. Typical waiting time around 2 to 3 weeks). While waiting, you can download the relevant forms and complete them. After your interview (where you have to hand over �13.50 to pay for a courier to return your passport), there's a long wait before you'll hear from the embassy. (One one page of their website, they state a minimum of 8 week. On another they quote a minimum period of 14 to 16 weeks). While you're waiting, your passport will be at the embassy, so you won't be able to travel abroad. (Note that even if you started the application process now, you might still be 'cutting it fine' to get your visa before November).
So, your best option seems to be simply to 'keep quiet' about the incident in Spain and answer 'No' to the question you're asked on the form you fill in on the plane.
Chris