Originally posted by normhead The guy who wants to shoot his son's basketball game in the local gym, the Tamron will still be the goto lens
I think you meant this as a general example, but after watching my son play basketball from 7 years old to 18 years old, I'll make a specific response. I never saw parents shooting DSLRs with big lenses at basketball games. Football and fastball, once in a while. Lots of high schools have a 5D and a 70-200 lens (always Canon brand) that either a photography student or a teacher will shoot with at games, and sometimes the staff photographer for the local newspaper shows up (with a more expensive version of the same kit), but parents quickly get frustrated trying to get good photographs of their child, partly because poor lighting and the challenge of getting in-focus shots defeats consumer level equipment, and partly because it is impossible to run your camera and follow the game at the same time. IQ is the least of anyone's concerns.
The other point I'll make is that a 70-200 isn't the ideal focal range on an APS-C body for sports within the confines of a gym. Assuming you are shooting from the floor, 50-135 would be much better, because if the action is in the closest quadrant of the court, 70mm is too long to get more than one player in the frame (and who wants a picture of a player standing by himself) and even shots of players under the basket at the opposite end of the court need minimal cropping at 135mm. I did some testing of my own with the 18-135 a year ago at a high school tournament and I didn't need to go wider than 47mm, which was too bad because it meant I couldn't get faster than f5.0. I'm not recommending the 18-135 for indoor sports, even a constant f4 would be better, but without top-notch AF from your lens and body combined, a faster lens isn't going to make much of a difference. Very challenging sport to photograph, volleyball is more predictable, soccer and North American style football don't change direction and distance as quickly as basketball.