I'm enjoying the debate too, it's interesting to hear how other people see it. My understanding of the LOTG is in line with mjp2's - I would think 2 players running after the ball are engaged in a challenge.
This sentence is also vague: “Careless” means that the player has shown a lack of attention or consideration when making a challenge or that he acted without precaution.
That implies that the lack of attention or consideration applies to making a challenge, but that acting without precaution doesn't. So even if you think that they weren't engaged in a challenge, you could still say that the defender was acting without precaution.
And if you don't agree with that interpretation, then you could still argue that he impeded Krishna's progress because as far as I see it, he did change the line he was running. But if that's what O'Leary was calling for then it wouldn't be a penalty - it would be an indirect freekick.
"Phoenix till they lose"