LONDON -- Guus Hiddink has joked that Chelsea "needed more rugby" in their style when he arrived in December and believes that footballers can benefit from training in more physical sports such as judo and boxing.
Chelsea have lost just one of 14 matches in all competitions since Hiddink succeeded Jose Mourinho on an interim basis, reaching the quarterfinals of the FA Cup and rising from 15th to 11th in the Premier League.
The revival has not always been serene, however -- Oscar and Diego Costa had to be separated by teammates during a particularly intense training session in January, while earlier this month Costa was forced to begin wearing a protective mask after having his nose broken during an accidental clash of heads with academy defender Fikayo Tomori at Cobham.
At the time Hiddink -- who practised judo and boxing as a teenager -- played down the altercation between Oscar and Costa as a confrontation between "two bulls," and he insists he likes his players to use their aggression and physicality to perform "on the edge" while staying within the rules.
Asked whether he thought Chelsea required a more physical edge when he took over in December, Hiddink joked: "They needed a bit more rugby!
"I was brought up as a physical teacher in the academies. I loved to do all the sports and people were brought up to practise those sports. When I was 18, 19, you get your physical education and I did boxing as well [as judo].
"It's a nice sport and if you train for boxing it's one of the toughest for endurance and aggression. Physically it's very tough but I liked it very much."
Hiddink says he has often organised warm-up games with a mix of handball and rugby rules during training sessions with previous teams to get his players accustomed to the physicality he wants from them on the football pitch.
"I love to see rugby also," he added. "When you have the combination of handball and rugby they are entitled to grab the guy who has the ball and make a wrestling move. No punching but it's also a mental part.
"If they are going into a fight -- within the rules -- in football, then I think you can gain a lot from other sports, including football.
"We installed and organised in my time at PSV a kind of wrestling with the youngsters, because on the pitch you have this physical contact and if you do those exercises you get a very good feeling of balance, how you can fight in your duels and so on. That's very important.
"I'm strongly in favour of wrestling [to develop footballers], especially in terms of how you fall. You're not afraid to fall and if you jump, you manage to land like a cat. If you have that experience as a youngster it will benefit you a lot."
Asked if he remained unconcerned by Oscar and Costa's confrontation because he likes his players to fight, Hiddink added: "Yes, but with respect. When they were threatening each other in the same second they knew deep down because they are friends, 'What are we doing?'
"I like when they go on the edge -- not fighting, but resistance. You feel the strong players in this league, and there is a lot of benefit when you are well equipped in balancing your physical fitness.
"It's not always that you have to be a big guy. When I see for instance Willian is not a big guy, but he is now fighting in duels defensively as well. He is smart to do so and he is willing to do so. That's modern football."
Asked if he still practises physical sports himself, Hiddink joked: "I box with my partner. She wins. You know in the end women are stronger!"