American rapper Akon was forced to jump into the crowd at his Melbourne concert last night to stop violent fans from brawling after the gig descended into chaos. Footage posted on YouTube shows the star making his way through the noisy crowd to security guards where he urged fans to "calm down". Four men, aged between 18 and 54, were taken to Royal Melbourne Hospital after being assaulted during the gig at the HiSense arena. A Victoria Ambulance spokesman said the men had su…