The following is just my opinion. I'm not a lawyer...
I have a domain name ****.in, which is related with a big world wide s-p-o.r.t.s event going to happen on next y.e.a-r.
If your domain relates to next year's Commonwealth Games, see
here.
If your domain relates to the 2010 World Cup, take note that FIFA owns many "FIFA" and "World Cup" trademarks (worldwide). I would view these as well-known marks and if your domain incorporates either of these terms then, IMHO, it's likely infringing on FIFA's trademark rights.
where should I check the same?
As you've registered a .IN domain, you'd need to check the
Indian trademarks register but that's not freely accessible.
I can see that in the US, FIFA owns trademarks such as SOUTH AFRICA 2010, WORLD CUP 2010 and FIFA etc. I wouldn't be surprised if FIFA registered similar marks in India. If it hasn't, it has likely acquired common law trademark rights. BTW, you can view FIFA's public guidelines regarding its official marks
here.
As mentioned by forgottenmemorie above, you can look at past domain arbitration decisions. If your domain does relate to the World Cup, then you'll see that FIFA has won domains such as fifaworldcup2010.com, fifaworldcup.net, fifa.tv (to name just a few).
But also I saw 100s of other domain names have already been registered with different combination and TLDs for this trademark.
Obviously, I don't know for sure which domain or trademark you're actually talking about, but perhaps the trademark owner hasn't caught up with these people yet. The other possibility is that the trademark owner is not aggressive about enforcing its trademark rights.
If you're unsure if it's a trademarked domain, then you should consult with a trademark lawyer.
If you come to the conclusion that you've registered a trademarked domain, then I think it's worth contacting your registrar to see if they can delete the domain registration (I don't know for sure if they will or can).