So, who planted bombs at Chinnaswamy?

This appears to be the handiwork of local pranksters and not terrorists as it is being out to be. At this stage the motive appears to be the unavailability of tickets.
Ajay Kumar Singh, director
General and Inspector General of Police, Karnataka, on Sunday

Though it is a terror attack we have no information about who the perpetrators were or what their motives were.
Shankar Bidari, police commissioner, Bangalore city

The mechanism of using loosely-packed ammonium nitrate with engine oil and ball bearings has been adopted by the Indian Mujahideen in the blasts that shook the country between 2005 and 2009. These blasts have the trademark of the IM. Their aim is to destabilise the economy of Karnataka.
IB Sources

We suspect that the explosions are the handiwork of a betting syndicate. Their aim seems be to disrupt IPL matches being held in Bangalore and ensure that the matches are shifted out of the city
VS Acharya, State Home Minister