There is a significant difference in photographing amateur and professional rugby. It is much easier to predict action with professional rugby. For example, line-outs they throw to the one jumping and the opposition may also compete whereas for amateurs, it can seem a little random. However, for premiership matches, you may need a press pass. Sadly my local premiership club will no longer allow photography with an interchangeable lens camera. Generally I have found that my 70 -200 is ideal from the touchline.
Dave