How do I stop this from happening?

[Chipmunk]

Conclusion- To force your inf to hold their fire you must slap a 15m arc AND a Hide order on them, otherwise they'll fire to defend themselves when the tank gets to within about 30m, because at that range they know the tank will possibly spot them anyway, as pic 4 showed.
(For the record, in some tests the TC became a casualty, in others he was unharmed)

I think DK wanted to know if there was a way to get the infantry to chuck their grenades at the tank when it entered their arc instead of firing small arms, not hold their fire altogether.