Thou shalt not kill.
Exodus 20:13; Deuteronomy 5:17
Man is such a paradox. He sins and is lawless. Yet he is a legalist at heart. Show me where “it is written!” If I have done what is written, well. If it is not written, I am free. Jesus addresses this tendency in the Sermon on the Mount with his repeated contrasts of “You have heard that it was said…but I say unto you.”
Reformed catechisms and theologians have been careful to expound the Ten Commandments with this sinful proclivity in view. The sixth commandment, as do all the others, says much more than the four English words say. Question 69 of the Westminster Shorter Catechism asks, “What is forbidden in the sixth commandment?” Answer: “The sixth commandment forbiddeth the taking away of our own life, or the life of our neighbor unjustly, or whatsoever tendeth thereunto.” The last three words are where battles could be fought: what exactly qualifies as “tending toward” death? Again, because we are legalists, we want to know exactly how dangerous something has to be before it is considered something “tending” toward death.”
As might be expected, question and answer 136 of the Westminster Larger Catechism gives a fuller answer:
Q. 136. What are the sins forbidden in the sixth commandment?
A. The sins forbidden in the sixth commandment are, all taking away the life of ourselves, or of others, except in case of public justice, lawful war, or necessary defense; the neglecting or withdrawing the lawful and necessary means of preservation of life; sinful anger, hatred, envy, desire of revenge; all excessive passions, distracting cares; immoderate use of meat, drink, labor, and recreations; provoking words, oppression, quarreling, striking, wounding, and whatsoever else tends to the destruction of the life of any.
According to the Westminster, the command forbidding murder also forbids any kind of physical harm that justice does not demand (i.e. parents are still required to discipline their children and civil authority is still required to punish evil).
Questions 105 through 107 of the Heidelberg Catechism are in substantial agreement with this:
105 Q. What is God’s will for you in the sixth commandment?
A. I am not to belittle, insult, hate, or kill my neighbor; not by my thoughts, my words, my look or gesture, and certainly not by actual deeds; and I am not to be party to this in others; rather, I am to put away all desire for revenge. I am not to harm or recklessly endanger myself either. Prevention of murder is also why government is armed with the sword.106 Q. Does this commandment refer only to killing?
A. By forbidding murder God teaches us that he hates the root of murder: envy, hatred, anger, vindictiveness. In God’s sight all such are murder.107 Q. Is it enough then that we do not kill our neighbor in any such way?
A. No. By condemning envy, hatred, and anger God tells us to love our neighbors as ourselves, to be patient, peace-loving, gentle, merciful, and friendly to them, to protect them from harm as much as we can, and to do good even to our enemies.
Reformed theologians echo the thought.
Predating both of the Catechisms above, Luther summarized man’s duty toward this commandments as: We should fear and love God so that we do not hurt or harm our neighbor in his body, but help and support him in every physical need.
When John Calvin turns his attention to explain this commandment in his Institutes of Christian Religion, he writes, “The purpose of this commandment is: the Lord has bound mankind together by a certain unity; hence each man ought to concern himself with the safety of all. To sum up, then, all violence injury and any harmful thing at all that may injure our neighbor’s body are forbidden to us.” (2.8.39)
The Reformers- at least two of the greatest- and Reformed catechisms- at least the three most well-known- interpret the sixth commandment in a Christ-like manner. The command prohibiting murder also forbids all physical harm and enjoins the protection of life.
With this understanding of the sixth commandment, how can any confessing Reformed Christian play, watch, or otherwise enjoy the game of football? Whether you are a Presbyterian who uses Westminster; or a Reformed who uses Heidelberg; or claim the term Lutheran or Calvinist; you are not being faithful to what you say you believe if you are investing time in football.
The game of football does physical harm to its participants. This element cannot be removed from the game. Furthermore, through the work of those doctors and scientists described in League of Denial, it is becoming clear that football literally kills it participants.
But we are legalists at heart. Football players do not get injured on every play. Not every football player will develop brain damage and die abandoned, penniless, and insane. Somewhere in the “tendeth thereunto” we can find all the allowance we need to enjoy watching men commit physical violence toward one another.
Broad Meadow 
My grandfather hated sports! He thought it was “dumb” for men to beat up on each other, and get paid for it!
Well this is a pretty quiet corner of the web so it is usually pretty safe to speak freely: but just in case any contrarians come along…
First of all, I don’t fault professional athletes at all for getting paid what they get paid. I think you can get to the pros on talent alone, but I don’t think you can stay there on talent alone. The vast majority of pro athletes are very hard workers. If I could get a job that paid 50,000 or a job that paid 10 million, I am pretty sure I know which one I would take.
Secondly, I don’t fault the owners either. Some owner have teams just for the fun of it, but I think most see it as it is: a business. Those guys didn’t get the hundreds of millions of dollars needed to buy a pro team by being idiots. They don’t keep the franchises by being idiots either.
With that out of the way… I am in increasing agreement with your grandfather. It is stupid. Just don’t lose sight of where the stupidity resides. The owners and the players all get that money from somewhere else- the people paying to watch.
Athletes get paid what they do because that is what we think they are worth. Doctors get paid more than pastors because we care more about our bodies than our souls. Lawyers get paid more than teachers because we care more about our reputation than our education. And athletes get paid more than all of them put together because we care more about being entertained than pretty much anything else.