Level Playing Field

In sports a "level-playing-field" is one in which all participants play not only on the same field, court, squared-ring, octagon, turf, etc., and utilize the same boundaries, but also adhere to the same rules. Also all judges, referees, umpires, scorers must also judge (score) the participants equally, ie without personal bias, based upon the rules of the sport.

With science the same should stand but with science being a broad venue the following caveat applies:

In any case, as Thomas Kuhn pointed out, debate about methodological rules of science often forms part of the practice of science, especially during times when established paradigms are being challenged. Those who reject the "teach the controversy" model on the grounds that ID violates the current rules of scientific practice only beg the question. The present regime of methodological rules cannot prevent the controversy for the simple reason that those rules may themselves be one of the subjects of scientific controversy.
page xxv of "Darwinism, Design and Public Education"

IOW the "rules" themselves may be creating an unlevel playing field. In which case those rules must be examined and their validity questioned.

And if one side is allowed to offer no more than speculative circumstantial evidence along with a heavy reliance on "sheer-dumb-luck", the other side should be accepted if it can also offer up the same level of data.