You can't overcome it because it is a human response. All professional players close their eyes just before impact because it is a human response to impact or expected shock. You can train yourself to keep your eyes open until the last moment but that is just a case of consciously forcing yourself to keep your eyes open while hitting the tackle-bag.
wear goggles
well its human nature to close your eyes before you make contact, i know this because i play rugby as well and when i first started playing i closed my eyes every time as i made contact with another plaer, but there is ways to train your self to keep your eyes open and the very last second but i cant say what they are because i don't know them, but i have gotten better on keeping my eyes until the last second before i make a tackle
