Why A gamma match taps the driven element (or tower) at a point some distance up from ground, running a parallel conductor from the feed point back down to the coax center conductor while the shield bonds to the grounded base. The tap height sets the resistive part of the impedance and a series capacitor in the gamma rod cancels the leftover inductive reactance, so a grounded tower used as a vertical radiator can be matched to 50 ohm coax without breaking the DC ground.
Watch out The beta or hairpin match is a shunt inductor used across a balanced driven element whose feedpoint is capacitive, typically on a Yagi, and it requires a split (not grounded) element. The double-bazooka is a broadbanding coaxial sleeve dipole design, not a tower feed method.
Grounded tower, shunt fed = Gamma. Gamma has one arm, like the Greek letter, tapping the tower above the base.