Do males have to push hard to inject sperm?
No. It just happens
If the pants are tight in the crotch area, then yes. The sperm in your scrotum survive at a temperature a couple degrees lower than your body temperature. This is why your sperm is stored away from your body. So tight pants and "whitie tightie" underwear push your scrotum against your body and raises the temperature of your sperm. This kills your sperm and gives you a lower sperm count.