‘And the Spirit of Yahweh came mightily on him and he tore him as he would tear a kid, and he had nothing in his hand.'
Calling on the One to whom his life was dedicated, and thus endued with the Spirit of Yahweh, Samson exerted his strength against the man-eater and with no weapon in his hand seized it and broke its neck as though it had been a young goat. It was his life or the lion's. From now on he knew that Yahweh was with him and would be his strength.
Samson's strength was clearly an unusual phenomenon. We need not doubt that he was of strong build, and even stronger than most men. But it would appear that because of his awareness of his special dedication to Yahweh he was at times able to arouse within himself a huge amount of adrenalin which made him invincible (we might to some extent compare him with the berzerkers, although the source of their strength was probably demonic). Once his dedication failed he found himself unable to arouse such strength.
‘But he did not tell his father or his mother what he had done.'
This may well have been through modesty, but the point behind this is that they did not know what he had done and so could not later give away the answer to his riddle.