R&B star Usher delivered a hit-heavy half-time show at Sunday's Super Bowl - with help from will.i.am, Alicia Keys, Ludacris... and a pair of roller skates. A disclaimer shown before the performance jokingly warned viewers it may cause "singing, dancing, sweating, gyrating, and possible relationship issues". It would go on to deliver on all fronts. Dressed in all-white and surrounded by a swarm of energetic dancers, Usher emerged on the stage at the Allegiant Stadium in Las Vegas and launched straight into one of his best-known songs, Caught Up. It kicked off a dynamic performance which took advantage of the...