Certain versions of MLB players in the game can have one or more Player Skills associated with them . Players with available skills will show skill icons on the right rim of their player portrait.  To see what skills the icons represent, tap the "i" information button in the top left of the player.
 

BATTERS' SKILLS

 
LHPvs Left Handed Pitchers
Boost to HIT & PWR against LHP

RHP
vs Right Handed Pitchers
Boost to HIT & PWR against RHP

TwoOuts
Two Out Hitter
Boost to HIT & PWR when 2 outs

RISP
Runners in Scoring Position
Boost to HIT & PWR when RISP

GarbageTime
Blowout
Boost to HIT & PWR when 4 runs ahead or behind

BonusGame
Bonus Games
Boost to HIT & PWR in Bonus games

SeasonGame
Season Games
Boost to HIT & PWR in Season Mode games

TournamentGame
Tournament Games
Boost to HIT & PWR in Tournament games

PrimeEventGame
Prime Event Games
Boost to HIT & PWR in Prime games

HeadToHeadGame
Head To Head Games
Boost to HIT & PWR in head-to-head games

WalkOffHeroGame
Walk Off Hero Games
Boost to HIT & PWR in Walk Off Hero games

TieGame
Tie Game
Boost to HIT & PWR when games is tied

BasesLoaded
Bases Loaded
Boost to HIT & PWR when bases loaded

BasesEmpty
Bases Empty
Boost to HIT & PWR when bases empty
 
EarlyInnings
Early Innings
Boost to HIT & PWR in first 3 innings

LateInnings
Late Innings
Boost to HIT & PWR in the 7th or later
 
CVC
Club vs Club Games
Boost to ALL stats in Club vs Club games

Hot
Hot Hitter
Boost to HIT & PWR after 1 hit in game
 
RunnersOn
Runners On Base
Boost to HIT & PWR when runners on
 
Close
Close
Boost to HIT & PWR when up or down 3 or fewer runs
 
Rally
Rally
Boost to HIT & PWR when down 3 or fewer runs
 
Leadoff
Leadoff
Boost to HIT & PWR when player is in the 1st batting position
 
Tie Game: Players with the Tie Game Skill receive boosted stats when the game is tied!
When a user acquires a player who has a skill, it will start off at skill level 0 and can be upgraded through normal gameplay.
 

PITCHER SKILLS

 
PitcherLHB
vs Left Handed Batters
Boost to all stats against LHB

PitcherRHB
vs Right Handed Batters
Boost to all stats against RHB

PitcherTwoOuts
Two Out Pitcher
Boost to all stats when 2 outs

PitcherRISP
Runners in Scoring Position
Boost to all stats when RISP

PitcherLateInnings
Late Innings
Boost to all stats in 7th or later

PitcherPrimeEventGame
Prime Event Games
Boost to all stats in Prime games

PitcherBonusGame
Bonus Games
Boost to all stats in Bonus games

PitcherSeasonGame
Season Games
Boost to all stats in Season Mode games

PitcherTournamentGame
Tournament Games
Boost to all stats in Tournament games

PitcherHeadToHeadGame
Head to Head Games
Boost to all stats in head-to-head games

PitcherRunnersOn
Runners On Base
Boost to all stats when runners on

PitcherEarlyInnings
Early Innings
Boost to all stats in first 3 innings

PitcherRally
Rally
Boost to all stats when down 3 or fewer runs

PitcherGarbageTime
Blowout
Boost to all stats when 4 runs ahead or behind

PitcherHot
Hot
Boost to all stats after 2 strikeouts in game

PitcherClose
Close
Boost to all stats when up or down 3 or fewer runs

PitcherFirstPitch
First Pitch
Boost to all stats on first pitch

FirstPitch
First Pitch
Boost to HIT & PWR on first pitch

XFactor (see FAQ on XFactor Skills)
XFactor