A young Serena Williams once refused to train until she got snacks, then smoked her hitting partner for an hour straight

• Serena Williams' longtime coach shared a story about bribing the legend to train as an 11-year-old.
• The coach, Rick Macci, said he motivated Williams to move her feet with the promise of snacks.

These days, Serena Williams — the 23-time Grand Slam champion widely considered the greatest player in modern women's tennis history — is motivated by the prospect of breaking tennis records and cementing her legacy in the sport.

But as a kid, Williams derived motivation from a simpler goal: getting snacks.

Rick Macci — a longtime coach for Williams and her superstar sister, Venus, dating back to when they were children — recently recounted a hilarious story about 11-year-old Serena negotiating her way into some treats during a tennis practice.

As Macci recalls, the Williams sisters were practicing side-by-side on a July day "and Serena's standing there in the corner... running the clock out." He instructed her to "move your feet," to which the younger Williams sister replied, "Why?"

"I said, 'What do you mean, why?!'" Macci said. "'You said you want to be number one!' And she goes, 'I will be number one.'"

"'Well, how can I get you to move your feet?'" the trainer insisted.

Some tasty treats, it turns out, were the answer.

"Rick, I'm really, really hungry," Macci remembered Williams telling him. "Can you have Scott go to the snack machine? I want some of those hot curly fries, a Snickers bar, a Pepsi, and on the way to work today, daddy drove by a stand on the corner ... and they were selling Green Day T-Shirts. Can you have Scott pick up one of those T-Shirts?"

"You see that girl on the court next — that tall, skinny girl?" Williams supposedly added, referring to her older sister. "I'll make her look slower than molasses."

So Macci sent this Scott character on a mission. He assembled array of "goodies" Williams requested — sans Green Day shirt — and brought it all back to the court.

"[Serena] has her snack for 15 minutes, goes back into the corner with the hitting partner, and for one hour straight — no water — popping the popcorn, extra butter, sweat is coming off this kid like Niagara Falls," Macci said. "[She's] ripping ground strokes, cross-court, down the line, just like a maniac. Bang! Bang! Bang!"

Then, Williams let her coach hear it.

"'Hey Rick!'" she called, according to Macci. "I turned around, and she goes: 'You better have that Green Day T-Shirt here in the morning.'"

"Cocky? Arrogant?" Macci added. "No, that's confidence."

Check out Macci's full retelling of the story below: