Rosenthal became an instant cult hero with his explosive start to his Liverpool career. He had been on trial at first division Luton Town where he scored two goals in three games but they couldn't broker a deal with Liege. The asking price was £500,000. Liverpool asked Liege if they could have a look and after only one reserve appearance he was signed on a loan. Rosenthal's full debut for the first team was against Charlton where he scored no less than three times. "Kenny was disappointed with Peter Beardsley and told me an hour before the game I’d be playing. After 10 minutes I scored with my right foot, then again immediately after half-time with my left and finally with my head after combining with John Barnes. The perfect hat-trick, I believe they call it." Four goals in the last six games of the season followed, his contribution vital to Liverpool's League triumph. Rosenthal's good form saw his asking price rise by 100% but that didn't deter Liverpool from tying up a permanent deal in late June after a work permit had delayed the completion of the move since he was offered a contract on 11 May 1990.
Rosenthal's dream start did not though secure him a starting place the following season and Liverpool's club record of eight straight wins from the start of the campaign kept him firmly in the reserves. Rosenthal scored 19 goals that season for the second-string but sadly his opportunities to shine in the first team proved few and far between. He did score a memorable last-minute winner in front of the Kop in the Merseyside derby on 20 March 1993. "The Rocket Man" stayed at Anfield until January 1994 when Tottenham paid £250,000 to secure his contract. He made a hundred first-team appearances for Spurs scoring 11 goals, including a sensational second-half hat-trick in a cup replay at Southampton in 1995. In August 1997 Rosenthal moved on a free transfer to Watford and helped them win the Second Division Championship. He retired as a player at the end of the 1998/99 season at the age of 35.
Rosenthal has continued to live in England following his retirement and is a football consultant. His younger son Tom is a promising footballer at Watford's Football Academy. Unfortunately. Ronny is often remembered for the often-replayed miss at Villa Park in September 1992 when he somehow managed to hit the crossbar at the Holte End after rounding the home 'keeper and being presented with the most open of open goals. It has been conveniently forgotten that Ronny did score later in that match although Liverpool lost 4-2. Ronny has special memories from his time at Liverpool that are
as delightfully quirky as his career was: "There was one incident I’ll never forget. We were warming up on the training field the morning after the Christmas party. Bruce Grobbelaar was leading the pack with Roy Evans behind him as we jogged around the pitch. Without warning, Bruce breaks wind and as Roy was right behind him, he was the first to run into it. It was so bad Roy keeled over and actually started vomiting," Ronny said. "All the other players then ran into it and keeled over or tried to escape the poisonous gas. It really was the most incredible sight I’ve ever seen on a training field."