Unlock the following by going to Options and then the Cheats screen and press X to bring up the area to enter them:
AFC North All-Stars:
NAOFRCTH

AFC South All-Stars:
SAOFUCTH
NFC West All-Stars:
ENASFSCT
AFC West All-Stars:
WAEFSCT
AFC East All-Stars:
EAASFSCT
NFC North All-Stars:
NNAS66784

NFC East All-Stars:
NNOFRCTH

NFC South All-Stars:
SNOFUCTH
No Fumbles (quick game mode only):
GlueHands

EA field:
EAField

Beat the Tutorials Team:
Xzibit

Legends
Hit the hotspots on each field. Once you unlock all the legends you unlock the legends team.

Darrell Green:
Hit a hotspot in 'The Backlot'

Jack Lambert:
Hit a hotspot in 'Royal Park'

Anthony Munoz
Hit a hotspot in 'The Cage'

Mean Joe Greene:
Hit a hotspot in 'The Tracks'

Bo Jackson
Hit a hotspot in 'Sportsplex'

Joey Browner:
Hit a hotspot in 'The Dig'
Sterling Sharpe:
Hit a hotspot in 'The Aqueduct'

Chris Carter:
Hit a hotspot in 'The Alley'

Randell Cunningham:
Hit a hotspot in 'Imperial Tower'

Mike Singletary:
Hit a hotspot in 'Second St. Station'