Were these brothers already at odds with each other? Or were they just practicing womb soccer?
These are the questions we must answer.
The boys were born a short time after their grandfather, Abraham, died.
Esau was described as a cunning hunter, and Jacob a plain man. This is not an insult - in fact the text is complimenting Jacob here. The Hebrew word used for plain meant whole, complete, or perfect.
That imagery probably falls in line with what you already know about Jacob, as the favoured son of Rebekah. It pretty much says so in verse 28. Isaac favoured Esau, the first born, and Rebekah preferred her youngest, Jacob.
One day, Esau said to Jacob, Feed me, I pray thee, with that same red pottage; for I am faint: therefore was his name called Edom.
And Jacob said, Sell me this day thy birthright.
And Esau said, Behold, I am at the point to die: and what profit shall this birthright do to me?
And Jacob said, Swear to me this day; and he sware unto him: and he sold his birthright unto Jacob.
Then Jacob gave Esau bread and pottage of lentiles; and he did eat and drink, and rose up, and went his way: thus Esau despised his birthright.
What's this about giving up and despising birthrights?
The primary point of this account is to show how little value Esau placed on the birthright. Perhaps he didn't understand its significance, although I am sure his parents weren't negligent in their teachings. Clearly his immediate physical needs were more important to him than the rights of the covenant.
And we see it all unfold in Genesis 27:1-33.
Esau asking Jacob for pottage - video still(source)
What I want you to understand is this: Even though Isaac originally thought he was blessing Esau, he did not change the blessing when he realized he had blessed Jacob. He didn't change the blessing one bit. He didn't even tack on a curse at the end for Jacob. Isaac, as a patriarch, recognised that the Lord inspired him to bless the right person.
This story helps us realize that the Lord inspires His servants to accomplish His will in spite of their weaknesses or incomplete knowledge of a situation.
I remember when we discussed this in class, I made the following example: I had just moved into a new ward (congregation) in a new stake. If I were to ask for my patriarchal blessing for the first time, I would naturally approach the patriarch in my new stake. As a newbie, he wouldn't recognised me or know me at all. But I would still received my blessing. You could even go in and say you're me, but we would receive our personal blessings.
“In the culture of this time period, the firstborn son received a “birthright,” which included the right to preside in the family and a double portion of his father’s goods and land when his father died. The birthright son then could take care of the rest of the family, including his father’s widow. The revelation Rebekah received concerning her two sons probably prepared her to understand that this tradition would not necessarily apply in their family. Receiving the birthright of the covenant did not come because of birth order but because of righteousness.” 
As an interesting side note ... throughout the Old Testament, Jehovah is repeatedly called the God of Abraham, Isaac, and Jacob. It is significant that you understand not only who Abraham was, but also why the Lord chose Isaac and Jacob to be the first of the house of Israel. They were all foreordained to their responsibilities, of course. But through their personal worthiness, however, they justified their callings in the covenant line.
Elder Bruce R. McConkie wrote:
“It appears that anciently under the Patriarchal Order certain special blessings, rights, powers, and privileges - collectively called the birthright - passed from the father to his firstborn son. (Gen. 43:33.)
In later ages special blessings and prerogatives have been poured out upon all the worthy descendants of some who gained special blessings and birthrights anciently. (3 Ne. 20:25–27.)
Justification for this system, in large part, lies in the pre-existent preparation and training of those born in the lines destined to inherit preferential endowments.” 
In the patriarchal order this birthright was passed from father to son, who was often, but not always, the eldest son. Righteousness was a more important factor than being the firstborn.
“Some people criticize Jacob for “taking advantage” of his brother; however, we do not know the whole story. The story does show what little value Esau placed on the birthright and the blessings of being the firstborn son in the covenant line of Abraham and shows that Jacob desired those blessings.” 
So ... just making sure we're all on the same page here ... Esau traded away something that would be of great value to him in the future (his birthright) for something of little value that could be obtained right away and satisfied an immediate appetite (hunger).
Do you think this happens today? People trading eternal opportunities and blessings for something worldly or something that satisfies an appetite?
After all had taken place, Esau didn't take this very well. He was a blessed man, never forgotten by the Lord, “... but like most of us he valued what he had lost after it was gone. ... He bitterly resolved to get revenge by fratricide when he saw the blessing of transmittal of the birthright actually confirmed upon the head of him to whom he had bartered the right to it.” 
What did alert and resourceful Rebekah do? She averted a double tragedy – if one murder the other, they would be executed by law. She then proposed to Isaac that Jacob be sent away to find a proper wife in her home land. Both she and Isaac understood that “their life’s mission would be frustrated if Jacob married as Esau had.” 
So Jacob went off to marry. And we all know how important that is ...
 Old Testament Seminary Manual
 Bruce R. McConkie, Mormon Doctrine, p. 87
 Old Testament Seminary Manual
 Rasmussen, Introduction to the Old Testament, 1:47, bold added