I think that this is happening with the 'Deliberate Knock-on'. Law 12.1e specifies that:
A player may not make an intentional knock-on or throw forward. Sanction: Penalty Kick. A penalty try must be awarded if the offence prevents a try that would probably have been scored.This is all quite clear, and has existed for at least the last 40+ years that I've been playing and refereeing the game.
We're now being faced - and not only in the professional game - with an assumption that a (failed) one-handed attempt to intercept a pass is automatically a deliberate knock-on. Every deliberate knock-on is a then taken to be professional foul (negative play) which is therefore held to be a yellow card offence.
The original assumption isn't justified in every case; often the pass that leads to the deliberate knock on is a 'miracle' pass that may not succeed anyway. The Laws of the game don't refer to professional fouls, and they clearly define the sanction for a tactic which can be used to cut out a sloppy pass. We should stop rewarding sloppy play - which is what a yellow card does in some of these cases.
I just watched the highlights of last weekend's Leicester Tigers v London Wasps match. Tommy Bell of Wasps attempted to pick off, one-handed a bad pass by Tigers that would have hit the intended receiver on the shoulder, admittedly, in the five metre zone, but the pass was terrible - it wouldn't have stuck anyway. Bell just failed to grab the ball with one hand - not a slap down. If the knock-on hadn't touched the intended receiver of the pass, it's quite possible that Bell would have regathered the ball and made a successful interception and counter-attacked. Instead, he received a yellow card.
At the Community Rugby level, I refereed a match recently where the passing by the home side was terrible, but each knock-on when attempting interception of a sloppy pass was called by them as deliberate. "Yellow card" was muttered in my hearing twice. After the third time, I had to have a word with their captain, and the appealing stopped. But it's quite clear that they thought that they could gain an easy advantage this way.
I think we need to get a grip and stop this nonsense. The Law is quite clear, and we need to make a proper judgment, for each occurrence, about whether an offence has been committed. Using one hand to try and reach a bad pass or a ball lobbed overhead is not prima facie evidence of intention to knock on. If the pass may well not have reached the intended receiver, it's also quite possibly difficult to intercept.
A Penalty Kick should only be given when it's absolutely clear and obvious that an intentional offence has been committed. A Yellow Card isn't specified by the Law and should only be given if there are additional aggravating circumstances not sufficiently satisfied by the award of a PK or a Penalty Try.
If the lawmakers decide that there is a shortcoming, let's go through the formal process to consider a change. But please, let's not invent new law on the fly and reward a failed 'miracle pass' with the sanction of a yellow card against the defender that gets in the way.