SEPTEMBER 13 ― According to the online dictionary, momentum is “the quantity of motion of a moving body, measured as a product of its mass and velocity”, or alternatively, and more straightforwardly, “the impetus gained by a moving object.”

The word is more commonly used, however, in a very different context from either of those strict definitions, denoting the growing likelihood of a sporting team or individual enjoying impending success.

They were gaining momentum; he had lost momentum; there was a change in momentum. All sports fans have seen and immediately understood those phrases hundreds of times, instantly apprehending the reference to change in the ebb and flow of a contest.

This weekend, momentum was being gained, lost and changed all over the place.

In Saturday’s big game in the English Premier League, Manchester City quickly established it and raced into a two-goal lead at Old Trafford, only to lose it when Claudio Bravo dropped the ball and Zlatan Ibrahimovic pounced.

Despite their newly-found momentum, Manchester United couldn’t do enough to salvage a point and Pep Guardiola walked away triumphant from his first meeting in England with Jose Mourinho.

A few hours later, the momentum which was slowly built by Alaves during the first half of their game at Barcelona eventually saw them take the lead, only for the hosts to regain it with an equaliser early in the second half.

But Alaves grabbed it back again to restore their advantage, and even the introduction of Lionel Messi, Andres Iniesta and Luis Suarez from the bench couldn’t give Barca sufficient momentum to rescue a point.

Then the NFL American Football season got underway in earnest on Sunday night, delivering its usual barrage of changes in momentum, including the Green Bay Packers getting the early momentum to take the lead, lose it to fall behind, and finally then grab it back to win.

And last but not least, Stanislaw Wawrinka faced the challenge of world number one Novak Djokovic in the final of tennis’s US Open and saw his opponent grab the momentum by taking the first set in a tie break.

Wawrinka wrestled it back to level and then forced the momentum to shift decisively in his favour to take a 2-1 lead, and although Djokovic attempted to respond it was too late ― Wawrinka had established too much momentum for him to fight back, and the Swiss took the title in four sets.

It’s a funny thing, this “momentum” word. Even if you didn’t see the sporting contests outlined above, the brief descriptions provided about the various changes of momentum experienced will allow you to gain a pretty good understanding of how they unfolded.

And that is despite the fact that the common and widespread usage of the word, in sporting terms, has very little to do with its actual meaning.

When we talk about an athlete gaining or losing momentum, we’re really not referring to “the quantity of motion of a moving body, measured as a product of its mass and velocity” at all.

What we’re trying to say ― and what is immediately understood ― is that this or that team or player is starting to play well or badly, therefore making his or her or their chances of success more or less likely.

If a football team has five shots on goal in the space of three minutes, we would say that they are gaining momentum and we would expect them to score quite soon. If a tennis player commits a series of unforced errors, we would say he has lost the momentum and fully expect him to lose the set.

But that’s slightly strange, because one piece of action in a sporting event in no way should necessarily lead to another similar piece of action. When a footballer takes a shot and misses, or a tennis player fluffs an easy volley into the net, the action is over. It’s a goal-kick or a new point, and what just happened shouldn’t really affect what happens next.

If the tennis player had previously been playing well and winning comfortably, one bad shot into the net shouldn’t change anything; if the football team had been dominated for an hour but then managed a brief period of pressure, it shouldn’t mean they have suddenly become the better team.

Yet somehow it does. How and why it does, we can’t be entirely sure, but it definitely does. One minute, you’re playing well, you’re in full control and everything looks good. The next, inexplicably, bang… you’ve lost your way, the opponent is on top and nothing you were previously doing is working anymore.

Why this happens remains a mystery. It’s probably mainly that elusive quality called confidence, which is notoriously capable of draining away or returning in spades at the drop of a hat. Tactical aspects can also be involved, opening up or closing down new opportunities, and the effects of tiredness or minor injuries can also be significant.

But really, nobody knows why these subtle shifts in the balance of power occur, as they do all the time, or how they can be effected or negated.

And so, because we don’t have any other better words for it, we call it “momentum” which, even though it has very little to do with the actual meaning of “momentum”, somehow fits the bill as a pithy one-word description for a range of unknowable factors contributing to an unexplained change in the dynamics of a sporting contest.

So if your favourite team is struggling in their next game, don’t worry ― they might just be able to get the momentum back.

* This is the personal opinion of the columnist.