1) "I'll get too big"
Team sport athletes, like Rugby players, would be in the weight room 2-4 times a week, at most. The type of training one should be doing and the volume is way below what one would have to do to prepare for a bodybuilding or figure competition.
Do some athletes experience a noticeable weight change? Yes, and usually in the form of healthy, lean muscle mass, which is only helpful in a contact sport like Rugby
2) "I don't want to get hurt"
Injuries from weight lifting occur when one is reckless or following a program/exercise that is not appropriate for their experience. A well-designed program that fits one's ability and accessible equipment can provide the correct progressions throughout the season/year.
3) "I don't have time"
An athlete does not have time NOT to strength train if they plan on playing a sport as intense as rugby. And not just for the ability to produce more force, but to help protect your body in a way that allows you to absorb more power in the tackles, rucks and scrums.
4) "I don't know what to do (where to start)"
Even gravity (bodyweight) is enough to start making a difference. Whether it's in your bedroom or at the neighbourhood park, there are plenty of ways to adapt specific movements to start making a difference.