Sentence:  With 73 minutes gone Rafael Márquez came on to add <WSD>ballast</WSD> at the back, appearing in his fifth World Cup aged 39 and with alleged links to drug trafficking, which he denies, on hold for now. And so they sat deep with a thin green line of five defenders ranged across their own penalty area as the game became a Mexican stand-off, attack versus defence. 
Meaning of the word marked with <WSD> tags:  That which gives, or helps to maintain, uprightness, steadiness, and security.