Orlando may have been victorious in his wrestling match with Charles, but his problems are by no means over. Although he is immediately showered with a chorus of praise not everyone is quite so enamored of him.
When Orlando reveals his true identity Duke Frederick laments that the young man should be the son of his arch-enemy Sir Rowland de Bois. As the dashing young blade Le Beau tells Orlando, he will get no praise from Duke Frederick. This is, after all, a man who bears grudges; a violent, vengeful man who's usurped his brother, Duke Senior, from his rightful place on the throne, and will subsequently expel his niece Rosalind from court for no other reason than that she is her father's daughter. If Duke Frederick can act this way towards his own flesh and blood, just imagine what he will do to the son of one of his most implacable foes.
As Le Beau points out, the Duke is due for another outburst of anger soon. Under the circumstances, then, it would be a good idea for Orlando to flee from this hateful tyrant as soon as possible, which he does. Orlando's in a dangerous situation here; from now on, he'll have to watch his back.