The in-game status pages have a lot of great information about your controls, so you can always check there for information.
Cars
RB - handbrake
RT - forward / gas
LT - brake to corner
X - headlights full beam and dimmed
L and R on d pad changes stations. Get little icons for each station
L to sound horn
Y to dive out of a moving car
RB in a cop car to use its computer
In a House
LB - watch TV can change channels
Y to save game
Free Roaming
A to run. tap A to sprint
Y to get in and out of a vehicle
X to jump over gaps (like between buildings)
X to climb over walls
LB to pick up a weapon on the floor
Cell Phone
up arrow - bring up phone
A to select phone book to call someone
Bowling
L dir for position, A to choose ready, Y for score, LB to quit
R down then R up to angle shot
R left or right to give touch while the ball rolls
Fighting
B - punch
Y - alt punch
X - kick
A - block
A tap - dodge
... then B or Y for counter move
to disarm - tap A to dodge then Y or B.
stun punch - get close to the guy and press b to hit him.
inner circle is his health bar. red is enemy. If it flashes, you can do a special execution move.
RB to take cover, RB again to leave cover
... while in cover, LT to lock on someone then RT to spin out from cover to get them.
Ladders
Y to mount
L directional to climb up or down
A to climb more quickly
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