It's similar to the metaphor "to be on a level playing field": this refers to games like football. A more obvious example of that idiom would be the game of snooker/pool, (if you have ever played this and the table is tilted, it makes a huge difference!). The phrase "on equal ground" is something that might have been used by military commanders in the past. For instance: "In our last battle you won, but my superior men fought uphill against your barely trained and ill-equipped men. We will now fight in the fields and, on equal ground, I will surely win". The idiom can now apply to any scenario when, as you have stated, two competing forces are "on the same level" or competing "FAIRLY". Eg. "Previously, you have had millions of dollars of support from corporate sponsors, which is why you have always won. With the recession, they've all abandoned you. We're on equal ground now and I am sure that we will win." "Although some teams look stronger than others, just remember that everyone starts on equal ground. This competition isn't over and it could still go anyone's way." --- Take care and good luck Wind :)!