Shimshon Hagibor was a spark of Esav’s neshamah. Therefore, Shimshon struck the Pelishtim specifically where he did as it says ויך ירך על שוק אותם, he struck them from calf upon thigh. This was in order to rectify the ירך of Esav, who is called נחשירכן. And of course we know that Yaakov was hit in the thigh by Esav’s malach.
Now, there are two types of nachash. Just as there is a nachash of tumah, impurity (the snake that caused the sin of Adam), correspondingly there is a nachash of kedusha. The Zohar teaches that Esav is from the side of the snake, from the side of tumah (in the word נחשירכן, we see the word נחש). In fact, Esav had a symbolic snake on his thigh. Don, who is referred to as a snake, is the one who counteracts Esav, as is evident from the fact that his son, Chushim, killed Esav.
Moving on, Shimshon is called a נחש, from the side of kedushah. A hint to this is found in חמת למו כדמות חמת נחש כמו פתן חרש יאטם אזנו — they have venom like the venom of a snake, like a deaf viper that closes its ears, where the end letters spell שמשון.
One last allusion is found in what is written about Shimshon: ויורידו אותו עזתה ויאסרוהו בנחשתים, they brought him down to Gaza and bound him with copper fetters. The word נחשתים can be seen as a contraction of נחש שתים, alluding to the two snakes: the snake of kedushah, represented by Shimshon, and the snake of tumah, represented by Esav, of whom Shimshon was a spark meant to rectify.
