Currently, one of the player is abusing the fact that when a player is challenged in ranked battle, no one else can challenge that player.

Specifically, for the past few days, he gets to 1st place 3-5 min before reward time, then have someone else challenge him so that he cannot be challenged by me and one of my group mate, who have the capability of knocking him off.

I'm not mentioning him by name because there is, frankly, no way for me to prove that this is what is happening. Thou quite frankly, now that ranked battle can resolve in 30s, it's unnatural for someone to be "tagged" for an entire 3-5 min near the end (and he doesn't lose as a result)

Instead, here is a few potential changes to counteract this. Note that any ONE of those would work, I'm merely providing options.

Note, the top ones are the easiest, the latter ones are harder. Thou there are other considerations. For example, #1 is super easy, but I don't expect it to happen.

1. Move pain in ranked shop to survival shop. The only reason we care, and he does this, is because now there is something useful in ranked shop. This change would effectively destroy the motivation.

2 Change reward structure so top 3 get same reward. This makes grabbing any top 3 spot equally good. And quite frankly, while one slot can be "tagged" by this mechanic, it's far more unlikely for all 3 to be tied down. So even if someone use this trick to guarantee their own rewards, at least other players have something to fight for.

3. Randomized reward time. This "camp at last second then challenge" thing is bad in and of itself. Even without this protection thing, the last second sniping isn't exactly healthy in and of itself. The same applies to space timed ranking as well. If, however, the reward time is random within a set window of 30-60 minutes, this would be far more unlikely.

4. Multiple reward batches. Specifically, instead of giving all reward at one time during the day. Make it give out 10 or 20% of the reward 10 or 5 times throughout the day, every (other) hour. Due to limited ranked battle attempts, it's rather unlikely for people to be able to "cheat" during all reward periods. This is, in a way, like qualifying for space time final, measuring consistent ranking as opposed to a single instance. Note that all rewards are divisible by 5 with most divisible by 10, so implementation can be made without changing reward at all or with only minimal change.

5. Must-skip within the last 10 min before reward time: right now, skip is an option. And the only way for this "tagging" to work is if the battle is not skipped, as otherwise the "protection" ends in 20-30 seconds. So if all battle automatically skip when it's close to reward time, protection won't be a thing. Snipping thou, still would.

6. Change it so that multiple player can challenge the same person. If this happens, if any of the challenger win, all the current on-going battles will be terminated. The attempt chance may or may not be refunded (this is up to you, so kind of 6a and 6b).

7. Make it so only #2 can challenge #1, only #3 can challenge #2 and only #4 can challenge #3. If a player who is previously ranked 2-4 who is currently challenging for higher position is challenged and lost(thus no longer have the position with the "right" to the current challenge), the fight is terminated, the attempt may or may not be refunded.
First, fact of the matter is that this is only a game design problem on the very high ranking. Because for anyone else, there are plenty of other options. So this change is mostly focused on the top ranking. With this new structure, a single "helper" will not be able to help #1 secure their spot. Because if the "helper" is in slot #2, #3 could knock him off, terminating the fight THEN go for #1. And if the helper is not in #2, whoever is in #2 can go after him. So for #1 to secure his spot with helpers, he'd have to control #2,3,4 and someone else to tag #4, this is rather unlikely. This would also solve the problem of someone who is highly ranked (top 3) being randomly knocked out of top 10 in the last few minutes, which have happened before. While still possible, it would take a series of losses which is far more unlikely considering that such a highly ranked individual is likely strong.

Yes, 7 still qualifies as "few". It does... right?

And for the record, yes, I am salty. To be quite honest, it doesn't impact me too much as I have trouble beating him, I'm ftp he is ptw, I only have 20-30% chance of beating him. But the fact that dirty trick is being used really irks me.