I think Paul was a boxer or a boxing fan. He specifically talks about fighting the good fight in both 1 and 2 Timothy. I highly doubt that Paul would use such an analogy if fighting was somehow inherently sinful.
The NT uses several athletic metaphors to illustrate the need for self-discipline: e. g.
"I do not
box as though beating the air; but I punish my body and enslave it, so that after proclaiming to others, I myself should not be disqualified (1 Corinthians 9:27)."
Several years ago, I attended my first and only boxing card at the Mecca of boxing, the MGM Grand in Las Vegas. As I booked my flight and hotel through my travel agent, she knew I was a local pastor and she railed against tourists who went to Vegas to attend violent UFC and boxing matches, wrongly assuming that I'd agree! I meekly kept silent about my plans to attend a boxing card during my week in Vegas.
The main event was the world welterweight championship fight between the idols of Mexico (Antonio Marguerito) and Puerto Rico (Miguel Coto). I have never seen such passion at a sporting event, including shoving and fights between the legion Mexican and Puerto Rican fans. I arrived early to watch the prelims at 2 PM. The pay-per-view card didn't start until 8 PM! Initially, there were no more than 100 fans in an arena that would eventually hold 10,000 fans. In front of me, 5 Mexican guys were getting drunk and I began to wonder if this was any place for a Christian. Then God found a humorous way to show me what He thought of my dilemma.
Sitting right behind me were 2 unaccompanied gorgeous young women. I overheard their conversation and was absolutely shocked by their topic. They were talking about all the things that were wrong with the United Methodist church that one gal used to attend--the liturgy, the music, the sermons, the Bible studies, etc. Both of them now attended Joel Osteen's church in Houston. After 20 minutes of this, I interrupted, smiling: "Your conversation greatly interests me because I'm a United Methodist pastor, and you make some good points." They laughed their heads off at this coincidence. Then when the next fight started, one guy got away with a low blow, and these church gals screamed and cussed at the ref! God seems to have a sense of humor! By the way, Marguerito knocked out Cotto.
On another day, I walked a couple of miles in the 100 degree heat and started to feel woozy; so I ducked inside the Circus Circus and sat down at a poker bar to cool off. I was feeling a tad guilty, sitting there, when a beautiful young black woman inexplicably sat next to me and we began to converse. She lamented that her boyfriend was being verbally abusive to her there. She used to sing in her United Methodist choir and wanted to study to become a physical therapist. But her plans all changed when her boyfriend got her pregnant. She quit church and gave up her vocational dream. Another gorgeous United Methodist gal, young enough to be my daughter (I'm single)! I witnessed to her, urging her to dump her boyfriend, go back to her church choir, and enter her dreamed physical therapy program. I assured her that she'd meet the right bright appealing young man in such a helping profession.
Absolutely stunned by my admonitions, she innocently asked, "Are you one of those angels unawares that the Bible says we might encounter?" I laughed and said I doubted guardian angels sweat like a greased hog like me!
We didn't realize that some men at the bar were staring at us. One scuzzy guy rushed forward, pointed his finger at me, and shouted, "Be careful, honey, I've seen his kind all over Vegas. I don't know what BS he's been dishing out, but you can't trust a word of it!" At first, I was offended, but then I thought about his reaction and realized that, to him, I must be some rich sugar daddy, spinning a yarn to pick up this babe. Then it hit me: God can be a loving presence anywhere, depending on our attitude; and He can use us anywhere if we are open to His promptings.