In a football game, suppose a team is down by two points with five seconds left, but they have the ball on their opponent's five yard line. They've stopped the clock and they're bringing in their kicker to attempt a field goal. It's an easy chip shot for him. He's perfect from that distance. We may debate which team is likelier to win (and, of course, I set up a situation where the team with fewer points is more likelier to win). Still, we say that the team with more points is winning.
In baseball, if the visiting team team scores a run in the top of the first inning, we say they're winning -- even though the home team hasn't batted yet.*
But I think we're doing it incorrectly. And I'm not saying that we should be indicating which team is likelier to win.
What does it mean to be winning? It means you are in the midst of a process, at the end of which you will have won. If we accept that, then a team is winning of they will ultimately win. It doesn't matter if that team is down by 40 million runs. Or goals. Or whatever it is that points are called in the sport they're playing. If they will ultimately win the game then they are winning.
Yeah, I know. I know. Words and phrases have meaning beyond their etymology. Since we all know what is meant by the simple question, "Who's winning?" there's no need to get all pedantic about it. Besides, communication would be hampered if we could never say who's winning until the game is over.
Still, every time someone asks me who's winning I want to say, "I dunno. Ask me after the game."
*Unless you're my sister, who will indicate which team is winning based on the score after the last completed inning**
**Unless the home team scores and goes ahead in the bottom of the inning, in which case she will acknowledge that they're winning because the visiting team cannot score again until the next inning