The back of Armor & Glory’s Camp Fit T-shirts, which read, “Put on God’s armor and receive His glory.” (Courtesy of Armor & Glory)

In 2013, a Bible-quoting high school football champ named Terrance Jackson, upset that most of the clothing options for his 3-year-old son were covered in skulls and crossbones, decided to start his own “inspirational apparel” company with a scripture-inspired name, Armor & Glory.

The family business hasn’t grown much since then, printing a few hundred shirts and spending nothing on marketing outside of a 1,500-fan Facebook page. But it recently received some major attention from America’s second-biggest sportswear empire, Under Armour, which demanded the small Maryland company change its name or face all-out legal war.

The trademark-infringement lawsuit filed this month in Maryland federal court has sparked a messy David-versus-Goliath battle in the fringes of American athletic wear and cast an unflattering spotlight on how fiercely the Baltimore-based giant intends to guard its brand and fight its way to the top.

But at a time when the fight for retail is getting tougher, the new lawsuit has also exposed just how messy protecting a trademark can get. Over the last year, Under Armour has taken aim at a series of companies mostly for using the word “Armor” in their names.

“It’s trademark bullying at its finest. I’m the little kid in the group and they’re trying to kick dirt on my new shoes,” said Jackson, 37, who said the name came to him one morning, from “the full armor of God” cited in Ephesians 6:11. “When God gave this [name] to me, I never thought once about those guys. We don’t even spell it like them.”

In its lawsuit, Under Armour, the mega-brand whose “Protect This House” slogan and army of star athletes helped it sell more than $3 billion of sportswear last year, says Armor & Glory’s name “is likely to cause confusion, mistake and deception” as to the two companies’ connection, which would “dilute the distinctiveness” and “further damage and irreparably injure” Under Armour’s brand.

[Under Armour’s athletes helped brand explode. Now comes the hard part.]

Under Armour’s attorneys at the Washington-based Finnegan, Henderson, Farabow, Garrett & Dunner, one of the world’s largest intellectual-property firms, wrote that Armor & Glory should have to destroy all products, hand over its domain name and any profits, and pay Under Armour’s attorney’s fees and damages of $100,000 or more.

“Under Armour has made a significant investment in fortifying all aspects of the Under Armour brand, including our intellectual property and our extensive family of trademarks,” the company said in a statement. “As a result, we are prepared to take all necessary actions to protect our intellectual property rights and the interests of our consumers and shareholders.”

Like Armor & Glory, Under Armour arose from humble beginnings, launched in 1996 as a maker of sweat-wicking shirts in founder Kevin Plank’s grandmother’s Georgetown basement. Since then, the company has exploded, speeding past Adidas to compete with Nike for the athletic industry’s billion-dollar throne.

“We have a chip on our shoulder,” Plank said last year, “and that chip doesn’t go away, because there’s not a finish line.”

Under Armour now spends tens of millions of dollars a year advertising its brand, putting out viral videos with sponsored athletes like Tom Brady, Misty Copeland and Stephen Curry. Last year, its “take-no-prisoners approach” helped the company win Advertising Age’s award for Marketer of the Year.

[When we were small: Under Armour]

But Under Armour has led a much subtler campaign to guard its dozens of trademarks, including ArmourChill, ArmourStorm, ArmourLoft, Offshore Armour and Baby Armour. Over the years, the company has amassed trademarks for virtually everything in the sports world, including camouflage vests, football girdles, lacrosse sticks, mouthpiece lanyards, rain trousers, snowboard mittens and toiletry kits.

Under Armour founder and CEO Kevin Plank started the athletics apparel giant in 1996 from his grandmother's basement. His advice to entrepreneurs: Put the pen down, work hard and get your product out there. (Jorge Ribas/The Washington Post)

Under Armour is far from the only company to protect perhaps its most valuable asset, its reputation, from potential threats. But when the company has felt its turf has been trod on, it has fought back forcefully in court. Under Armour has sued Body Armor, a sports-drink company; Salt Armour, a Florida fishing-apparel firm; and Ass Armor, maker of shock-absorbing snowboarding shorts.

In 2013, Under Armour even sued Nike, saying the Big Swoosh’s social-media motivations, like “I will sweat while they sleep,” copied Under Armour’s “I Will What I Want” campaign. The case was eventually settled under undisclosed terms. (Under Armour has also been on the other side of the suit: Last year, Adidas sued Under Armour for infringing on its fitness-technology patents.)

The expensive court battles have not always just been about the name. In February, Under Armour sued Skechers, claiming the shoemaker’s commercial “slavishly copies” Under Armour’s ad because of its “similarly lit, close-up images … of athletes in cavernous warehouses … taking on rigorous physical workouts, such as climbing a pegboard, whipping heavy ropes, boxing and jumping hurdles.”

Armor & Glory chief executive Terrance Jackson, left, and vice president of grassroots marketing Ed Tomlin. (Courtesy of Armor & Glory) Armor & Glory chief executive Terrance Jackson, left, and vice president of grass-roots marketing Ed Tomlin. (Courtesy of Armor & Glory)

Armor & Glory is an incredibly small target for Under Armour. Though Jackson said he wants Armor & Glory to become a “global brand,” it has so far made less than $100,000 in revenue since 2013 — about 0.003 percent of Under Armour’s sales just last year. The company’s online store sells $20 shorts and $25 shirts designed largely for a core Christian audience, with slogans like “Be spiritually attractive” and “Put on God’s armor and receive His glory.”

“We’re babies, man. We’re in the infant stage,” Jackson said. “It’s about building a movement to celebrate the power of God. It’s not even a big financial thing right now, it’s about winning the souls.”

Armor & Glory has also hosted youth football camps and “life-skills boot camps,” which Under Armour said in its suit were too similar to its own football events. The company also said Armor & Glory was adding to the confusion for customers by linking its apparel with sports stars: In a post on Armor & Glory’s Facebook page, Minnesota Vikings running back Adrian Peterson can be seen wearing the company’s branded compression tee.

Under Armour has pledged no end to its litigation. In an e-mail shared with The Washington Post, Under Armour’s former trademark attorney, William J. Morris III, tells Jackson that “continued use of the mark will not go unchallenged” and guarantees “an expensive and time-consuming legal battle.”

[How winning the Masters made Jordan Spieth into Under Armour’s hero – and Nike’s nightmare]

That might require more money than Armor & Glory has at hand: The company on Sunday launched a crowd-funding campaign to help support its legal defense. (By Wednesday, it had raised $100 of its $50,000 goal.)

So why not just change their name? Ed Tomlin, Jackson’s partner and a former director of football development for Under Armour (who says he left on good terms), says “it’s a matter of principle and a matter of faith.” The name, he added, “was inspired by God. … To turn our backs now would be like we were being disobedient.”

And Tomlin offers a business upside to the battle: Demand for the brand “has increased dramatically” since the cease-and-desist letters began.

“I don’t think anything happens by coincidence,” Tomlin said. “People love their underdogs.”