The above video comes from tipster Graeme (naturally), who explains it thusly:

It's of a fight between Chris Ashton (in the white jersey) of the Northampton Saints and Manu Tuilagi of the Leicester Tigers (in the extremely non-tiger-like stripes) from Saturday's Premiership semi-final. On first view it looks like a case of handbags at 10 paces [see] but the slo-mo replay reveals some Rocky-style shit. The action starts at around 0.25.

Leicester defeated Northampton, 11-3, to advance to its seventh straight Aviva Premiership Rugby final, which will be contested at Twickenham on 28 May. They may play without Tuilagi, who only received a yellow card for the punch, but could face citation for his behaviour. Northampton will face Leinster in the Heineken Cup final in Cardiff, for a consolation championship, on 21 May.

Leicester Tigers-Northampton Saints Highlights [YouTube]