Coaches sometime think that clock management is part of their job description as a soccer coach. It isnt. Yet some will engage in questionable tactics late in a match in waste time. Understand that wasting time falls under two categories: Those tactics which are legal and those which are not.
Legal tactics include kicking the ball out of play including kicking the ball far out of play. This may not rise to the level of unsporting behavior but is gamesmanship as players are permitted to kick the ball out of play. The intelligent referee will detect this tactic and may simply announce that while they are welcome to employ this tactic, that he will be adding time to make up for the lost time. Its amazing how quickly the teams quit using this approach once the referee takes control.
Another legal tactic is the frequent call for substitutions, often always for the far side midfielder. Again, teams have this privilege. Referees can remind players to hustle on and off.
Illegal tactics of time-wasting include kicking the ball away after the whistle has blown for a free kick. Or picking the ball up and carrying it. Or picking it up for a throw-in then calling another player over to take the throw.These can be sanctioned with a yellow card for delaying the restart. But generally the players will heed a warning if the referee would talk to them.
Tournament rules often require a "running clock" which prevent referees from adding time. In these cases, referees may have to step it up a notch. Substitutions are still permitted but only if the player is waiting at the halfway line. If the players are being lazy at the substitution, taking their time on or off, the ref can ask the player to depart the field at the closest point and certainly remind players to hustle. Players taking their time can be carded for delaying the restart.