John Gill Commentary Genesis 26:20

"And the herdsmen of Gerar strove with Isaac`s herdsmen, saying, The water is ours. And he called the name of the well Esek, because they contended with him." — Genesis 26:20 (ASV)

And the herdmen of Gerar strove with Isaac's herdmen About the well which was dug in the valley; and this shows it was near Gerar or at least was upon the border of the country, and so it was a disputable point to whom it belonged:

saying, the water [is] ours; though the well was dug by Isaac's servants, yet they laid claim to the water, pretending it was their ground, being on their borders:

and he called the name of the well Esek: which signifies "contention": the reason of the name follows,

because they strove with him; wrangled, contended, and disputed with him about whose right it was.