The 38-year-old veteran lock has been a captain on a British & Irish Lions tour, played 94 times for his country and made 268 appearances for Munster but now he is skipper of Worcester Warriors in English Premiership.
The two-time Heineken Cup winner signed a one-year contract extension at Sixways earlier this season, having originally joined from Munster in September 2015.
And despite his vast experience, the Cork native says stepping out opposite Irish opponents is still the biggest challenge in the game.
“They are the ones that I always find the toughest. I don’t mind playing against any of the English teams and knocking lumps out of them but when you are looking over and it’s one of your own across the way I find it kind of tough,” said O’Callaghan.
“It’s about respect. The big one for me was that I never knew the value of Simon Easterby until I played against him.
“I remember when you were playing with him you were wondering what Simon was getting up to, but when you were playing against him he was involved in everything and he earned respect.”
Worcester have made a dreadful start to their Premiership campaign where they lost all six games and lie bottom of the standings.
But in Europe they kicked of Pool 5 in the Challenge Cup with a bonus point win over Brive and O’Callaghan believes his team can go far in the competition. “It was really weird for me but Europe was seen in a different light over here last year. Thankfully Gary Gold (Director of Rugby) doesn’t see it that way. He sees it as a competition to go out and do our best in,” said O’Callaghan.
“Last year was a rotation and I found that so alien that Europe wasn’t the pinnacle. Thankfully it’s back to being up there.”
Worcester will lose Gold at the end of this season, when he heads off to coach the US national side. But O’Callaghan says the younger players are being given a chance and that’s vital for the future of the team, and the players trying to break through.
“Gary is giving the younger guys a go and it’s about trying to make sure they know that you don’t get a whole lot of opportunities like that,” said O’Callaghan. There aren’t a whole lot of teams in the Premiership that will take guys as young as we are going to go this season, and throw them in. They are going to make mistakes, but that’s what we all did. It’s funny, I remember chatting with ROG about the approach I know myself we were allowed to make mistakes but now there are so many guys and so many options. There was no one else when we were younger.
“ROG was saying about that kick he missed against Northampton, if that happens a modern young fella now you look somewhere else because there are so many of them. Munster could look nowhere else. That’s the same with us, there are younger guys, you have got to help them fulfil their potential but know they don’t get a whole lot of shots at it.”